Apparatus and method for rapid reliable electrothermal tissue fusion and simultaneous cutting

ABSTRACT

A method of electrothermally fusing together pieces of tissue at an interface and simultaneously cutting the fused tissue along a linear path through the interface, including: compressing the tissue pieces together at the interface sufficiently for fusing the tissue pieces together and for cutting the fused tissue pieces in the linear path through the fused tissue at the interface; delivering an impulse of electrical power of no greater than 4.0 seconds time duration which contains sufficient energy to fuse the tissue pieces together at the interface and to simultaneously cut the fused tissue; converting the electrical power impulse into thermal energy applied at the interface; and regulating the temperature of the thermal energy applied at the interface in a range of 200° C. to 320° C. while fusing and simultaneously cutting the tissue pieces at the interface by controlling characteristics of the electrical power impulse.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/701,884, filed on Feb. 1, 2007, the contents of which is relied uponand incorporated herein by reference in its entirety, and the benefit ofpriority under 35 U.S.C. §120 is hereby claimed. This application isrelated to inventions for an Apparatus and Method for Rapid and ReliableElectrothermal Tissue Fusion, described in U.S. patent application Ser.No. 11/701,857, and for an Tissue Fusion Instrument and Method to Reducethe Adhesion of Tissue to its Working Surfaces, described in U.S. patentapplication Ser. No. 11/701,858, both of which are assigned to theassignee of the present invention. The disclosures of theseconcurrently-filed U.S. patent applications are incorporated herein intheir respective entireties by this reference.

FIELD OF THE INVENTION

This invention relates to electrothermal tissue fusion, and moreparticularly, to a new and improved electrothermal apparatus andelectrothermal method that seals or fuses tissue while simultaneouslycutting or separating the tissue with the application of a shorttime-duration impulse of electrical energy which creates relatively hightemperature heat that is applied to squeezed-together tissue pieces. Thetissue sealing and simultaneous cutting occurs quickly, and the seal isof high integrity to resist failure while the cut results in awell-defined, substantially linear separation of the tissue through thesealed area.

BACKGROUND OF THE INVENTION

Coaptive electrothermal tissue fusion or sealing involves theapplication of force and electrical energy to heat compressed tissuesufficiently to join together separate pieces of tissue. Electrothermaltissue fusion avoids the need to manually suture or tie-off tissues orvessels during a surgical procedure. The tissue is fused or sealed toprevent blood or other fluid loss so that thereafter the tissue may becut or incised. Thus, the usual purpose of sealing or fusing tissue isto allow cutting of the tissue adjacent to the fused area during thesurgical procedure.

In most cases, sealing the tissue and thereafter cutting the tissueadjacent to the sealed area is a desired and efficient way to perform asurgical procedure. Tissue cutting has therefore been combined withelectrosurgical tissue fusion, in order to obtain efficiency andconvenience. However, the tissue cutting is almost universallyaccomplished by use of a blade or other mechanical cutter rather than bycutting through the application of electrosurgical energy. The commontypes of mechanical tissue cutting devices have had the effect ofcompromising the effectiveness of the tissue seal or fusion. Withoutadequate tissue sealing or fusion, tissue cutting becomes substantiallyirrelevant because a failure to adequately seal or fuse the tissueoffers no advantage over the typical manual procedures of suturing ortying off vessels or cutting tissue with a scalpel. Therefore, achievingand maintaining effective and reliable tissue fusion is a prerequisiteto tissue cutting.

Although the exact details of the physical chemistry involved in tissuefusion are probably not completely understood, it is believed that theheat denatures chains or strands of tissue proteins in the separatepieces of tissue and the pressure causes the denatured protein chains toreconstitute or re-nature across the interface between the tissuepieces. The reconstituted proteins chains interact and intertwine withone another to hold the previously-separate tissues pieces together.

Collagen is one type of protein chain that appears to play an importantrole in tissue fusion. Collagen, also known as tropocollagen, consistsof three polypeptide protein chains that form a triple helix. Theseprotein chains are grouped or tangled together to establish significanttissue structure and strength, as is observed in blood vessels andligaments. Applying heat to the tissue to raise the temperature to about60-70° C. causes the protein chains to become disordered, disassociated,separated and untangled from the triple helix.

Elastin is another type of protein chain that appears to play animportant role in tissue fusion. Elastin a collection of polypeptideprotein chains that are individually and randomly cross-linked with eachother to form a fibril. Fibrils are grouped or tangled together to forman elastin fiber. Upon the application of heat to raise the temperatureto about 120° C., the elastin fiber becomes disassociated into adisordered collection of individual polypeptide chains, fibrils andfibers.

The heat which causes denaturation of the collagen and elastin chainsalso appears to create unfavorable molecular interactions among thecomponents of the denatured proteins, resulting in a relatively highfree energy state. Atoms with the same electrostatic charge, andhydrophobic and hydrophilic regions of the protein chains, begin tointeract and create repulsive forces. Force must be applied at theinterface between the tissue pieces during fusion to overcome therepulsive forces and to achieve more favorable interactions of theproteins chains thereby reducing the amount of free energy. Force mustalso be applied at the interface to maintain the denatured proteinchains in physical proximity with each other so that they willreconstitute and join the tissue pieces together.

Although this theoretical model of tissue fusion is understandable,reliable tissue fusion is difficult to achieve on a consistent basis.Fusing blood vessels is of particular concern, because vessel fusionduring a surgical procedure is the primary use of tissue fusion at thepresent time. Fused blood vessels that fail or leak after the conclusionof surgery lead to internal bleeding. Internal bleeding usually requiresa second operation to gain access to and seal the leaking vessel, whichinduces further trauma and risk to the patient.

One prior art type of electrosurgical tissue fusion involves bipolarelectrosurgery. The tissues are compressed between two jaws of aforceps-type instrument. The jaws also serve as electrodes to conducthigh-voltage radio frequency (RF) current through the compressed tissue.Heat is generated from the RF current flowing through the resistance orimpedance of the tissue, and that heat denatures the chains of protein.

Certain difficulties arise when using bipolar electrosurgical tissuefusion. The voltage between the jaws which compress the tissue and serveas electrodes is typically several thousand volts. The distance betweenthe jaws is relatively small when the tissue is compressed. Therelatively high voltage can create arcs which jump the small distancebetween the jaws and penetrate the tissue adjacent to the jaws,particularly toward the end of the fusion procedure when the tissuebetween the jaws dehydrates and its impedance increases. The arcs enterthe tissue in minuscule spots and destroy or weaken the tissue at thosespots. Under conditions of prolonged application of RF power in thismanner, which is typical with bipolar electrosurgical tissue fusion, thearcing can actually perforate the tissue adjacent to the fused area,thereby rupturing the tissue and destroying any sealing effect from thesealed area if there are a significant number of ruptures. This isparticularly the case when sealing vessels, because a typical failuremode of vessels sealed with bipolar electrosurgery is a leak or rupturein the wall of the vessel adjacent to the sealed area.

The RF current inherently flows through the tissue in a somewhat randomor uncontrollable pattern depending on the point-to-pointcharacteristics of the tissue and many other factors. As a consequence,uniform heating of the tissue is impossible to control. Thenon-homogeneous distribution of heat over the area to be fused causesthe protein chains to denature and reconstitute in a variable andnonuniform manner. The nonuniform denaturation and reconstitution leadsto fused tissue areas of variable, nonuniform and somewhat unpredictablestrength.

Assessing when to stop the delivery of RF current during bipolarelectrosurgical tissue fusion is difficult. Applying either too much ortoo little RF current leads to seals that are more likely to fail. Theapplication of too much RF current creates an excessive amount of heatwhich drives chemical reactions that appear to oxidize or burn thetissue and change the nature of the protein chains, thereby diminishingtheir ability to reconstitute and create effective seals. Overly-heatedtissue at the sealed area or adjacent to the sealed area increases theprobability of a failure because the tissue has become brittle and lackspliability due to excessive dehydration, thereby contributing tocracking and breaking. In contrast, prematurely stopping the delivery ofRF current prevents an adequate amount of denaturing of the proteinchains which, in turn, prevents an adequate amount of reconstitution ofthe proteins chains, thereby diminishing the strength of the seal.

Control systems have been developed to attempt to address the problem ofapplying too much or too little RF power during bipolar electrosurgicaltissue fusion. Such control systems monitor some event associated withthe application of electrical power to the tissue, typically theimpedance. Monitoring the tissue impedance is based on an expectationthat some change indicates the occurrence of appropriate sealingconditions. However, it is believed that no reliable relationship existsbetween tissue impedance and the formation of a consistently reliableseal.

Another problem with bipolar electrosurgical tissue fusion is that thealternating aspects of the RF electrical energy inherently results inless energy application per unit of time. The alternating aspects of theRF energy application are by nature a pulsed or alternating current (AC)energy application, as opposed to a continual energy application. Thetissue must withstand relatively high voltages, but the amount of powertransferred is not commensurate with the high voltage due to the pulsedor AC application of the RF current. The effect of the pulsed oralternating RF energy application is that more time is required totransfer an equivalent amount of energy compared to the transfer ofenergy delivered at a sustained peak value. The typical maximum powerdelivery with a widely used RF tissue fusion device is approximately 115to 350 Watts per square inch (18-54 W/cm²).

Electrothermal instruments have also been used for tissue fusion.Electrothermal instruments have heating elements within jaws that gripand compress the tissue. Electrical current is conducted through theheating elements to generate the heat that is applied to the compressedtissue. As with bipolar electrosurgery, previous electrothermalinstruments have produced varying and inconsistent tissue fusionresults, possibly as a result of an ineffective control system orcontrol functionality based on misperceptions relating to tissue fusionphysiology, including the perceived limitation of not heating the tissueabove the 120° C. point where elastin protein chains denature. Theprevalent view is to avoid elevating the temperature of the tissuebeyond the 120° C. point where elastin protein chains denature, becauseit is believed that temperatures beyond that point are destructive tothe proteins chains. Consequently, all presently known tissue fusiontechnologies attempt to limit the tissue temperature to no more thanapproximately 120° C., and many tissue fusion technologies limit thetemperature of the tissue to approximately 100° C. to avoid creatingsteam.

The typical approach used to combine tissue cutting and fusion is toincorporate a mechanical blade with the applicator of the RF or thermalenergy. The electrodes of the RF applicator, or jaws of theelectrothermal applicator, create the fusion. Once the fusion iscomplete, the blade is advanced in grooves or slots formed in theelectrodes or jaws to sever the fused area of the tissue, usually whilethe electrodes or jaws maintain pressure on the tissue. Such mechanicalcutting systems are prone to sticking or jamming. Usually the mechanicalblade is relatively thin and therefore has a tendency to distort whilecutting, which may cause friction and sticking as it advances in thegrooves or slots. The fluid and small pieces of tissue at the surgicalsite may also interfere with the intended movement of the mechanicalblade.

The mechanical action of the blade severing the fused area of tissuealso has the tendency to induce forces on the sealed area and theadjacent tissue, which typically compromises the effectiveness of theseal. Advancing the mechanical blade through the sealed area canseparate the sealed area sufficiently to create a fluid leak and mayeven crack or otherwise destroy the sealed area to create a fluid leak.In certain circumstances, the mechanical blade can become so stuck orjammed to prevent release of the tissue from between the electrodes orjaws. Such a circumstance is particularly serious in minimally invasive(endoscopic or laparoscopic) surgery because the closed minimallyinvasive procedure has to be converted to an open surgical procedure togain access to the stuck applicator and release it from the tissue.Converting a closed minimally invasive surgical procedure to an openprocedure induces substantial unexpected trauma on a patient, andunexpectedly prolongs the duration and risk associated with the surgicalprocedure.

A further disadvantage of mechanical cutting is that the blade must beadvanced in a linear direction, making it impossible to cut on a curve.Many surgeons prefer to use instruments which are curved, particularlyin minimally invasive procedures where visualization is difficultbecause of a lack of stereoscopic vision. A curved electrode or jaw iseasier to observe from the monoscopic perspective of minimally invasivesurgical procedures.

Attempts have been made to electrothermally cut tissue simultaneouslywhile fusing the tissue, but all such known attempts have provedunsuccessful or impractical. In general, tissue cutting whilesimultaneously fusing the tissue has involved delivering energy into thetissue for a considerable length of time. The prolonged energy deliveryhas apparently heated the tissue to the point where essentially completedehydration of the tissue occurs and causes the tissue to become crisp,brittle and friable, like a potato chip. The tissue simply reaches apoint where the sealed area disintegrates or crumbles.

Such prolonged heating has the effect of inducing thermal spread intothe adjacent tissue, which compromises the strength of the seal and theunsealed adjacent tissue areas. The brittleness of the tissue causes itto separate or crack in a non-defined or non-controllable manner, whichmay extend the crack to the adjacent tissue walls and compromise ordestroy the seal and create a leak. Moreover, the separation through thesealed area is essentially non-defined because of the relatively largearea of total dehydration and the inability to control where thedehydrated tissue will crack or disintegrate. Consequently, known tissuefusion and simultaneous cutting procedures result in cutting which ismore of the nature of ill-defined tissue obliteration rather than linearcutting along a desired path which surgeons prefer in order to avoiddamaging more tissue than is necessary during the overall surgicalprocedure.

Although the principal concern of tissue fusion and cutting in a singleprocedure is creating reliable seals that hold on a long-term basis,another very important practical consideration is an ability to createthe seal and perform the cut quickly. A typical surgical procedure willinvolve sealing many blood vessels at the surgical site. The typicaltime required by known electrosurgical tissue sealing devices to createa single seal is about 5-12 seconds. When also simultaneouslyelectrothermally cutting the tissue in the manner described, the entireenergy application extends from 30 to 60 seconds. When mechanicallycutting the tissue after it has been fused, an additional 5 to 10seconds is required in order to advance the mechanical blade through thefused area, providing that no sticking or jamming occurs. A considerableamount of time is therefore consumed in making each single-procedureseal and cut. Considering that a typical surgical procedure may requiresealing and cutting scores of vessels, a considerable amount of thetotal overall surgical procedure time is consumed by vessel sealing andcutting.

Moreover, because of concern about the reliability of the vessel seals,the typical practice is to create two sequential seals at each severedend of the vessel. The theory is that if the first or upstream sealfails, the second or downstream seal becomes a redundant backup toprevent fluid leakage. The time to create the primary and backup sealsis more than twice the amount of time required to create a single sealwhen the time for repositioning and observing the quality of each sealis taken into account. Further still, double seals must be made at bothends of each severed vessel if there is concern about leaking from theseals created at opposite ends of the vessel which is cut. Thus, aconsiderable amount of time is consumed during the surgical procedure bysealing vessels and cutting them. The time consumed by cutting andsealing vessels extends the time required to accomplish the entiresurgical procedure, or alternatively, detracts from the time availableto accomplish other activities during the surgical procedure.

SUMMARY OF THE INVENTION

The present invention creates reliable seals of good integrity whilesimultaneously cutting the tissue, and does so in a considerably shorteramount of time than known single-procedure tissue sealing and mechanicalcutting techniques or known tissue sealing and simultaneous cuttingtechniques. The present invention delivers a short impulse of arelatively high amount of electrical energy to create the heat appliedto fuse or seal the tissue while simultaneously cutting the fusedtissue. Creating a reliable seal having good structural integrity whilesimultaneously cutting the seal is achieved with an electrical powerimpulse having a typical duration of about 2.0 or less seconds, and inmany cases about 1.5 seconds or less. In certain exaggeratedcircumstances, a time duration of the electrical power impulse mayextend to about 4.0 seconds, but this circumstance is unusual. Theamount of energy delivered is sufficient to elevate the jaw temperatureat the interface between the sealed and cut tissues to between 220° C.and 320° C. The relatively short time duration of the energy impulse andthe resulting high temperature quickly create an effective, reliable andconsistent seal followed by severing the tissue along a well-definedpath through the sealed area.

Cutting or separation of the tissue occurs along a well-definedseparation or parting line or path that may be linear in a straight orslightly curved sense. The separation line is established by theconfiguration of the jaws which grasp and compress the tissue duringsealing and simultaneous cutting. The linear nature of the separationpath or parting line is displaced sufficiently from the adjoining fusedtissue areas to avoid compromising the strength or integrity of theadjoining fused areas. The separation or parting is accomplishedsimultaneously with the tissue fusion, so adverse forces on apreviously-formed fused tissue area are avoided, thereby avoiding theproblem of weakening the integrity of the sealed area by subsequentcutting.

The short time duration of the high temperature application does notaffect the ability of the protein chains to renature and thereafterreconstitute in a strong reliable bond, even though the temperaturecreated is considerably higher than the typically-regarded appropriatetemperature for tissue fusion. The short impulse of relatively high heatis believed to effectively dehydrate or desiccate polar water moleculesfrom binding sites on the protein chains without so dehydrating thetissue as to substantially compromise its pliability, thereby permittingmore and direct interactions between the protein chains at those bindingsites, resulting in stronger direct interactions between the proteinchains, increased affinity between the chains and increased strength ofthe fusion between the tissues at the interface. However, the shortimpulse of energy does not so dehydrate the sealed tissue to cause it tolose its pliability and strength and thereby contribute to a leak orseal failure. The cutting occurs while the tissue is sealed and remainsslightly pliable, thereby facilitating well-defined separation whileavoiding adverse forces on the sealed tissue areas that might negativelyaffect the strength of the seal.

The seal and simultaneous cut created by the relatively short impulse ofhigh energy become effective immediately, allowing the compression forceon the tissue to be released almost immediately after delivering impulseof energy, without requiring a cooling-off time period. The short amountof time required to create the simultaneous cut and seal, and theavoidance of a subsequent cooling-off period or a mechanical cuttingtime period, greatly diminish the amount of time required to completeeach simultaneous cut and seal procedure.

The quick delivery of energy forms an effective seal withoutsignificantly destroying, cracking or substantially adversely affectingthe strength of the tissue adjacent to the seal along the separationline where the cut occurs. Consequently, the sealed and other tissueadjacent to the separation line retains its natural strength and isunlikely to fail, unlike the typical prior art electrosurgical tissuesealing and cutting procedure which spreads considerable thermal energyto the adjoining tissue. The thermal spread to the adjoining tissue isbelieved to destroy or diminish the strength of the adjacent tissue andthe sealed area, making them susceptible to rupture from physiologicalpressure and from mechanical severing.

The sealed areas have a consistent strength which is significantlygreater than the normal physiological pressure applied on the sealedareas. The strength and integrity minimizes or virtually eliminatespost-operative bleeding. The reliability and integrity of the sealsdiminishes or eliminates the need for double seals for redundancypurposes. However, under circumstances where double seals are preferred,the characteristics of the seal created assure that a failure of theprimary upstream seal will still confine the fluid to the vessel so thatthe redundant downstream seal will have the opportunity to function asan effective backup.

In accordance with these and other features, one aspect of the inventionis an apparatus for fusing together pieces of tissue at an interface andsimultaneously cutting the fused tissue along a linear path through theinterface. The apparatus comprises an instrument and a power controldevice. The instrument includes jaws with working surfaces and amovement mechanism which moves the jaws toward one another to compressthe tissue pieces together at the interface between the workingsurfaces. The working surfaces are formed of ceramic material and have asmoothness defined by an Ra of 0.40 microns or less. The movementmechanism has a capability for transferring sufficient force to achievea compressed tissue thickness sufficient to fuse the tissue pieces atthe interface, which in the case of blood vessels is 0.05 mm to 0.10 mm,followed by further compressing the tissue pieces at the interface to azero thickness to cut the fused together tissue pieces. The powercontrol device delivers an impulse of electrical power to the jaws whichcontains sufficient energy to fuse and simultaneously cut the tissuepieces along the linear path at the interface within no greater than 4.0seconds after the electrical power impulse is initiated. The powerimpulse creates thermal energy and maintains a temperature of thethermal energy applied to the interface in the range of 220° C. to 320°C.

Another aspect of the invention is an apparatus for fusing togetherpieces of tissue at an interface and simultaneously cutting the fusedtissue along a linear path through the interface. The apparatuscomprises an instrument and a power control device. The instrumentincludes jaws with working surfaces and a movement mechanism which movesthe jaws toward one another to compress the tissue pieces together andto obtain a zero separation distance between the working surfaces of thejaws to simultaneously cut the compressed and fused tissue pieces alongthe linear path. The power control device delivers an impulse ofelectrical power to the jaws which contains sufficient energy to fusethe tissue pieces together and to simultaneously cut the fused tissuepieces at the interface by creating a temperature applied to theinterface in the range of 220° C. to 320° C. within the time duration ofthe electrical power impulse.

A further aspect of the invention is a method of electrothermally fusingtogether pieces of tissue at an interface and simultaneously cutting thefused tissue along a linear path through the interface. The methodinvolves compressing the tissue pieces together at the interfacesufficiently for fusing the tissue pieces together and for cutting thefused tissue pieces in the linear path through the fused tissue at theinterface, delivering an impulse of electrical power of no greater than4.0 seconds time duration which contains sufficient energy to fuse thetissue pieces together at the interface and to simultaneously cut thefused tissue in a linear path through the fused tissue at the interfacewithin the time duration of the electrical impulse, converting theelectrical power impulse into thermal energy applied at the interface tofuse the tissue pieces and to simultaneously cut the fused tissue piecesin the linear path through the interface, and regulating the temperatureof the thermal energy applied at the interface in a range of 220° C. to320° C. while fusing and simultaneously cutting the tissue pieces at theinterface by controlling characteristics of the electrical powerimpulse.

Preferably, the time duration of the electrical power impulse is nogreater than 2.0 seconds. The invention is particularly applicable tofusing apposite walls of a vessel to form an occlusion in a lumen of thevessel while simultaneously cutting the vessel.

Certain further aspects of the invention involve one or more of thefollowing features: releasing the interface immediately aftertermination of the electrical power impulse, elevating the temperatureof the thermal energy applied at the compressed interface at a rate ofbetween 150° C. per second to 500° C. per second from energy containedin the electrical power impulse, producing an energy density in therange of 388 W per square centimeter to 465 W per square centimeter ofarea of the compressed interface from the electrical power impulse,forming electrical power impulse from direct current and conducting thedirect current power impulse to a heating element within each jaw,releasing compression of the interface after fusion and simultaneouscutting by moving the working surfaces away from the fused and cutinterface with the working surfaces extending parallel to one another,releasing compression of the interface without inducing shear forces onthe fused and cut interface, and separately regulating characteristicsof the electrical power impulse delivered to the heating element withineach jaw to regulate the temperature of thermal energy applied by theworking surface from each jaw separately.

A more complete appreciation of the present disclosure and its scope,and the manner in which it achieves the above and other improvements,can be obtained by reference to the following detailed description ofpresently preferred embodiments taken in connection with theaccompanying drawings, which are briefly summarized below, and to theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an electrothermal tissue fusion or sealingand simultaneous cutting or separation apparatus which incorporates thepresent invention and which comprises a tissue fusion and simultaneouscutting instrument, shown in a perspective view, and a power controldevice, shown in block diagram form, which are used to seal andsimultaneously cut a vessel, shown in perspective.

FIG. 2 is an illustration of the use of the tissue fusion andsimultaneous cutting apparatus shown in FIG. 1 to fuse and cut a vessel.

FIG. 3 is an enlarged side elevational view of distal arms and jaws ofthe instrument and a cross-sectional view of the vessel shown in FIG. 1,before compressing the vessel when fusing and simultaneously cutting it.

FIG. 4 is a view similar to FIG. 3, showing compression and fusion ofthe vessel.

FIG. 5 is a view similar to FIG. 4, showing separation of the vesselafter it has been fused.

FIG. 6 is a perspective view of the tissue fusion and simultaneouscutting apparatus shown in FIG. 1 after the vessel has been fused andcut as shown in FIGS. 4 and 5.

FIG. 7 is a perspective view of the tissue fusion and simultaneouscutting instrument shown in FIGS. 1, 2 and 6, with portions broken awayto show internal details of a parallel jaw movement mechanism and ahandle locking and release mechanism, and with certain electricalconductors shown broken away.

FIG. 8 is an enlarged partial perspective view of top and bottom distalarms and top and bottom jaws of the instrument shown in FIGS. 1-7.

FIG. 9 is a perspective view of a bottom jaw shown in FIG. 8.

FIG. 10 is an enlarged longitudinal and vertical cross-sectional view ofthe bottom jaw shown in FIG. 8.

FIG. 11 is a transverse cross-sectional view of the bottom jaw shown inFIG. 10, taken substantially in the plane of line 11-11 shown in FIG.10, and illustrating a heating element embedded in the bottom jaw.

FIG. 12 is an end elevational view of one form of the working surface ofthe bottom jaw shown in FIG. 9.

FIG. 13 is an end elevational view of another form of the workingsurface of the bottom jaw shown in FIG. 12, which is an alternative tothat shown in FIG. 12.

FIG. 14 is a more detailed block diagram of the power control deviceshown in FIG. 1, showing in block form certain aspects of the tissuefusion and simultaneous cutting instrument shown in block diagram formin FIG. 1.

FIG. 15 is a block diagram illustrating the functionality of atemperature control feedback routine executed by a processor of acontroller of the power control device shown in FIG. 14.

FIG. 16 is a graph of temperature versus time illustrating thetemperature of jaws of the tissue fusion instrument when sealing avessel with a 2.0 second time-duration impulse of electrical energy.

FIG. 17 is a graph similar to FIG. 16, illustrating the temperature ofthe jaws of the tissue fusion instrument when sealing a different vesselwith a 1.5 second time-duration impulse of electrical energy.

FIG. 18 is a longitudinal cross-sectional view of a partial vessel whichhas been sealed with a prior art technique, viewed orthogonal to a flatsurface of the sealed area of the vessel, illustrating an edge-sealleak.

FIG. 19 is a longitudinal cross-sectional view of a partial vessel whichhas been sealed with a prior art technique, viewed parallel to flatsurfaces of the sealed area of the vessel, illustrating a mid-seal wallleak.

FIG. 20 is an enlarged partial perspective view of sealed areas of avessel created as shown in FIGS. 4 and 5.

FIG. 21 is a longitudinal cross-sectional view of the partial vesselshown in Fig., taken in a plane substantially perpendicular to a flatsurface of the sealed areas.

FIG. 22 is a longitudinal cross-sectional view of the partial vesselshown in FIG. 21 with increased fluid pressure applied in the vessel ona left-hand side sealed area.

FIG. 23 is a longitudinal cross-sectional view of the partial vesselshown in FIG. 21 with greater fluid pressure applied in the vessel onthe left-hand side sealed area and illustrating initiation of mid-sealseparation of the sealed area.

FIG. 24 is a longitudinal cross-sectional view of the partial vesselshown in FIG. 23 illustrating complete mid-seal separation of the sealedarea.

FIG. 25 is an enlarged partial longitudinal cross-sectional view of avessel, illustrating two prior art longitudinally-spaced sealed areas.

FIG. 26 is a longitudinal cross-sectional view similar to FIG. 25,illustrating a prior art edge-seal leak also shown in FIG. 18.

FIG. 27 is a longitudinal cross-sectional view similar to FIG. 25,illustrating a prior art mid-seal wall leak also shown in FIG. 19.

FIG. 28 is a longitudinal cross-sectional view related to FIG. 25,illustrating a mid-seal separation, also shown in FIGS. 23 and 24, of afirst one of two sequential sealed areas in accordance with the presentinvention.

DETAILED DESCRIPTION

The present invention is incorporated in an electrothermal apparatus 20shown in FIG. 1. The electrothermal apparatus 20 is used to fuse or sealbiological tissue, such as a vessel 21, while simultaneously cutting orseparating the biological tissue, by use of a handpiece or tissue fusionand cutting instrument 22. Proximal handles 24 and 26 of the instrument22 are moved or squeezed together, which causes a parallel movementmechanism 28 (FIG. 7) of the instrument 22 to move distal arms 30 and 32of the instrument 22 toward one another with parallel closing movement.Jaws 34 and 36 are attached to the distal end of the arms 30 and 32.Working surfaces 38 and 40 of the jaws 34 and 36 contact, squeeze, forceand compress the vessel 21 when the jaws 38 and 40 and the distal arms30 and 32 move toward one another, as shown in FIG. 2. Beforecompression, a lumen 42 within the vessel 21 is unobstructed and notoccluded as shown in FIG. 3. Movement of the jaws 34 and 36 toward oneanother forces and compresses walls 44 of the vessel 21 into appositionwith one another at a tissue interface 46 shown in FIG. 4.

An impulse of electrical energy from a power control device 48, shown inFIGS. 1 and 2, is delivered to a heating element 49 (FIGS. 8 and 10-13)embedded in each of the jaws 34 and 36, upon compressing together theapposite walls 44 of the vessel 21 at the tissue interface 46. Theheating element 49 converts the electrical power to heat, and the heatis conducted from the working surfaces 38 and 40 to elevate thetemperature of the compressed apposite vessel walls 44 at the interface46. The temperature of the vessel walls 44 is elevated to apredetermined set point temperature within the range of 220° C. to 320°C. where tissue fusion and simultaneous cutting occurs while the jaws 34and 36 compress the apposite vessel walls 44 against one another untilthe working surfaces 38 and 40 contact one another and thereby sever orcut the sealed vessel walls 44 at a well-defined line along thelongitudinal dimension of the working surfaces 38 and 40. The forceapplied from the working surfaces 38 and 40 in contact with the appositevessel walls 44 is sufficient to squeeze the fully compressed and heatedapposite vessel walls until an essentially zero dimension gap, i.e.complete contact, between the working surfaces 38 and 40 of the jaws 34and 36, respectively, is achieved. This force required to achieve anessentially zero space or gap between the working surfaces is usuallygreater than 150 Newtons (N), but may fall within the range of 110 N to150 N.

The heat first denatures and disassociates the protein chains at theinterface 46 of the compressed apposite vessel walls 44 at the interface46. The denatured protein chains immediately reconstitute or re-natureacross the compressed tissue interface 46 to fuse or seal the vesselwalls 44 together at a sealed area 50 (FIGS. 6 and 20). The sealed area50 occludes the lumen 42 and prevents fluid normally confined within thelumen 42 from passing from the vessel 21. Continued compression furthersqueezes the sealed area 50 until the heat essentially destroys thetissue in a well-defined separation line 51 through the sealed area 50and causes the vessel 21 to separate or part at the separation line 51(FIGS. 6 and 20). Immediately after the impulse of electrical power isterminated, the handles 24 and 26 are moved away from one another, whichcauses the arms 30 and 32 and the attached to jaws 34 and 36 toseparate, releasing the vessel 21 which has been cut or severed at theparting or separation line 51, as shown in FIGS. 6 and 20. The tissuefusion and simultaneous cutting procedure is typically complete in 1.5to 2.0 seconds.

The heat is disbursed substantially uniformly throughout the jaws 34 and36 and across the compressed tissue interface 46 (FIG. 4) at the sealedarea 50. The tissue walls 44 are continually compressed until a zero gapor contact is achieved between the working surfaces 38 and 40. The heatand the continued compression destroys the-tissue in a well-definedlinear manner between the working surfaces 38 and 40 at the separationline 51 to separate the vessel 21 after it has been sealed and occludedin the sealed areas 50 adjoining the separation line 51.

The jaws 34 and 36 are formed of high thermal conductivity material,preferably ceramic material such as aluminum nitride, thereby achievinga substantially uniform temperature on the tissue squeezed between theworking surfaces 38 and 40. The tissue interface temperature isapproximately equal to the temperature of the jaws 34 and 36 due to therelatively thin amount of tissue compressed between the jaws.

The working surfaces 38 and 40 of the jaws 34 and 36 are smoothed orpolished, preferably to an, Ra of less than 0.15 microns. Jaws withworking surfaces which have this degree of smoothness prevent the tissuefrom sticking to the jaws during fusion, despite the high relativelyhigh temperature of the jaws against the tissue. By avoiding sticking,the integrity of the seal created is not damaged or its strengthcompromised from separating the jaws 34 and 36 after the seal has beenformed, as would be the case if the tissue stuck to the jaws.

The impulse of electrical power delivered from the power control device48 has a power density of greater than 1500 Watts per square inch(W/in²) (233 W/cm2) of the working surfaces of the jaws 34 and 36, andpreferably in the range of 2500 W/in² to 3000 W/in2 (388 W/cm2 to 465W/cm2). This power density is considerably higher than the typical powerdensity of 115-350 W/in² (18-54 W/cm2) obtainable from a prior art RFtissue fusion device that is presently widely used The impulse ofelectrical power raises the temperature of the jaws at a preferable rateof about 500° C. per second or more. An impulse of electrical power ofthis magnitude is sufficient to increase the temperature of the jaws 34and 36 to about 220° C. to 320° C. very quickly after application of theimpulse. The tissue fusion and cutting occurs over the 1.5-2.0 secondpreferred time duration of the electrical power impulse, allowing thejaws 34 and 36 to be separated or moved apart from one another torelease the sealed area immediately after terminating the electricalpower impulse.

The time required for achieving a reliable seal with high integrityagainst leaking and simultaneously cutting the tissue is related to theamount of tissue squeezed between the working surfaces, the type oftissue involved and the temperature applied to the tissue. Largervessels, thicker walled vessels or larger amounts of tissue typicallyrequire longer sealing times and/or higher temperatures. Effective sealsand cuts of typical small to medium vessels of 2-3 mm diameter areachieved with electrical impulses of less than 1.5 seconds duration,while seals of larger vessels in the neighborhood of 7-8 mm diameter areachieved with electrical impulses of about 1.5-2.0 seconds duration.Electrical impulses having a time duration of up to about 4.0 secondsare effective in some situations involving very large vessels, moremassive amounts of high-density tissue, low thermal conductivity tissue,and/or lower temperatures.

Achieving consistent, reliable seals and simultaneous cuts on a widerange of different sizes and types of vessels provides a significantprocedural advantage over known prior art tissue sealing apparatus.Known prior art vessel sealing techniques are believed to require atleast 5-12 seconds of power application before a seal is formed and thenthe time required to advance a mechanical blade slowly through thesealed area and then withdrawn before the vessel can be released. Theadvancement of the mechanical blade must progress relatively slowly toavoid distorting the sealed area and compromising the integrity of thesealed area which could lead to a leak. In general, 5-10 seconds isrequired for manual advancement and retraction of the blade, providedthat the blade does not become jammed or stuck. Those known prior artelectrothermal systems which attempt sealing and simultaneously cuttingrequire times of at least 30-60 seconds to perform both sealing andsimultaneous cutting, and then the cutting is more akin to raggedobliteration rather than a well-defined linear separation. Thus,simultaneous cutting and sealing is accomplished with the presentinvention considerably more quickly compared to known prior arttechniques. In addition, the seal created by the present invention hasenhanced integrity and resistance to failure after cutting, compared toprior art seals.

The vessel 21 exemplifies biological tissue which is sealed andsimultaneously cut with the present invention, and the lumen 42 of thevessel 21 exemplifies a lumen, duct, passageway, chamber or gap orseparation which is to be permanently bonded, occluded, sealed, fused orjoined. The actions of bonding, occluding, sealing, fusing or joiningtissues are collectively referred to herein as fusion or sealing. Theaction of separating the tissue after it has been fused or sealed isreferred to herein as cutting or separation. In addition to the vessel21, which may be an artery or a vein, other specific examples ofbiological tissue which may be fused or sealed and thereafter cutinclude fallopian tubes, bile ducts, tissue surrounding an aveoli or airsac in the lung, the colon or bowel, or any other tissue where surgicalligation might be performed. In most but not necessarily all of thecases where tissue fusion or sealing and simultaneous cutting isperformed, the purpose of sealing or fusing the tissue is to confine afluid or other bodily substance and its associated flow within apassageway which is either defined by or closed by fusing or sealing andthe purpose of cutting the tissue is to excise tissue for surgicalpurposes. Therefore, in accordance with a naming convention followed inthis detailed description, the walls 44 of the vessel 21 are examples ofapposite pieces of biological tissue which are fused or sealed, thelumen 42 of the vessel 21, is an example of a passageway which ispermanently occluded or closed or defined by sealing the apposite walls44 at the interface 46 of the vessel 21, and an example of cutting thetissue occurs through the sealed area 50 along the separation line 51with the apposite walls 44 sealed at the interface 46 occluding thelumen of the vessel on opposite sides of the separation line 51.

The smoothness of the working surfaces 38 and 40 of the high thermalconductivity jaws 34 and 36 contributes to creating seals of highintegrity and cutting the tissue in a short amount of time. Smoothworking surfaces 38 and 40 release the fused and separated tissue fromthe jaws 34 and 36 without sticking when the jaws separate (FIG. 6),despite the relatively high temperature of those jaws when compressingthem against the tissue during fusion and simultaneous cutting.Preventing the tissue from sticking to the jaws as they separate avoidspulling the fused vessel walls apart, which could destroy or weaken thesealed area. Consequently, the fused interface of the vessel walls willhave substantially all of the integrity and strength created by thefusion process, and that integrity and strength is not diminished byseparation forces when the jaws separate. The smooth working surfaces 38and 40 decrease the risk that the seal will ultimately fail.

Tissue sticking to the working surfaces of the heated jaws is asubstantial problem in prior art devices. If the tissue sticks to thejaws as they separate, the integrity of the fused interface at thesealed area of the vessel will be compromised by the tendency to pullthe sealed vessel walls apart at the fused interface 46. Even if thefused apposite vessel walls are not separated at the fusion interface,the separation force may weaken the walls enough to allow the naturalfluid pressure within the lumen or passageway to eventually separate thevessel walls and create a leak.

Quickly achieving seals of high integrity while simultaneously cuttingthe tissue is also facilitated by an even distribution of compression,force or pressure across the squeezed vessel walls 44 at the interface46 (FIG. 4). The even force or pressure distribution across the tissueinterface 46 is obtained by parallel movement of the working surfaces 38and 40 toward one another when compressing the vessel 21 (FIGS. 4 and5). The parallel movement mechanism 28 causes the jaws 34 and 36 andtheir respective working surfaces 38 and 40 to move parallel to eachother when opening and closing and compressing and releasing the vessel.The parallel movement of the jaws 34 and 36 avoids introducing shearforces on the sealed tissue interfaces 46 of the separated vessel pieces(FIGS. 4 and 5) when the jaws separate. Shear forces have the effect ofweakening the sealed tissue interface and diminishing the strength ofthe seal created on each of the separated vessel pieces.

Details of the parallel movement mechanism 28 of the instrument 22 areexplained and shown mainly in conjunction with FIG. 7 but also in FIGS.1, 2 and 6. The proximal handles 24 and 26 pivot with respect to oneanother in opening and closing movements. The parallel movementmechanism 28 transfers the force created by the opening and closingmovements of the handles 24 and 26 into parallel opening and closingmovement of the distal arms 30 and 32. The parallel opening and closingmovement occurs over the range of movement where the tissue iscompressed between the working surfaces of the jaws during tissue fusionto the point where the working surfaces 38 and 40 contact one anotherwith a zero distance gap there between. The parallel movement avoidsintroducing adverse shear forces on the fused tissue and creates evenforce and pressure on the tissue when compressed for fusion and cutting.

The parallel movement mechanism 28 is enclosed within a housing 52(FIGS. 1, 2 and 6). The housing 52 is formed by a rear wall member 54and a front closure member 56 which includes integral top, bottom andside wall portions which enclose internal components of the parallelmovement mechanism 28. Openings are formed in the integral side wallportions of the front closure member 56 to allow the handles 24 and 26and the arms 30 and 32 to extend into the housing 52.

The top handle 24 is integrally attached at its distal end to a block62, and the block 62 is rigidly attached to the rear wall member 54 bypins 64. The bottom arm 32 is formed integrally with the rear wallmember 54. Thus, both the top handle 24 and the bottom arm 32 arerigidly connected relative to the rear wall member 54. Thus, the tophandle 24 and the bottom arm 32 do not move relative to one another orrelative to the rear wall member 54 or the housing 52. Only the bottomhandle 26 and the top arm 30 and jaw 34 move relative to the stationarytop handle 24 and the bottom arm 32.

The bottom handle 26 is pivotally connected to the rear wall member 54at a pivot pin 66. The bottom handle 26 pivots around the pivot pin 66.When the top and bottom handles 24 and 26 are separated or moved towardone another, only the bottom handle 26 possesses the freedom to pivot.The pivot pin 66 is located slightly proximally from the distal end ofthe bottom handle 26.

The top arm 30 has a flange 68 integrally attached to its proximal end.The flange 68 extends generally parallel to the rear wall member 54. Asthe top arm 30 moves upward and downward, the flange 68 moves upward anddownward with the top arm 30 within the housing 52 between the rear walland front closure members 54 and 56.

A rail 70 is rigidly attached to the rear wall member 54 by pins 72. Therail 70 extends perpendicularly relative to the extension of the bottomarm 32. The rail 70 projects outward from the rear wall member 54 towardthe flange 68. A guide block 74 is attached to the flange 68 by pins 78.The guide block includes a center channel 76 which conforms to thecross-sectional shape of the rail 70 and which movably receives andsurrounds the rail 70. The size of the center channel 76 permits aslight clearance on each the three lateral sides of the rail 70 whichextend outward from the rear wall member 54. The guide block 74, flange68 and the attached top distal arm 30 are therefore movable along a pathdefined by the rail 70 and relative to the rear wall member 54.

The rail 70 is oriented perpendicularly to both the top and bottom arms30, and therefore movement of the top arm 30 maintains the same parallelangular relationship with the bottom arm 32. The rail 70 has substantialstructure to withstand the torque applied to the distal end of the toparm 30 during tissue compression to maintain the same relative angularrelationship of the top arm 30 with the bottom arm 32.

One end of a link 80 is pivotally connected at the distal end of thebottom handle 26 by a pivot pin 82. The other end of the link 80 ispivotally connected to the flange 68 by another pivot pin 84. Upon theclockwise (as shown in FIG. 7) pivoting movement of the bottom handle 26relative to the top handle 24, the distal end of the bottom handle 26transfers upward force through the link 80 to the flange 68. The flange68 moves upward along the rail 70, and causes the connected top arm 30to separate from the bottom arm 32. Consequently, an opening movement ofthe bottom handle 26 relative to the top handle 24 causes an openingseparation movement of the top arm 30 relative to the bottom arm 32. Agap or separation is created between the working surfaces 38 and 40 ofthe top and bottom jaws 34 and 36 by the separation movement of thebottom arm 32 relative to the top arm 30.

Closing the top and bottom handles 24 and 26 moves the distal end of thebottom handle 26 downward, causing the link 80 to move the flange 68downward along the rail 70. The top arm 30 moves downward toward thestationary bottom arm 32, thereby closing the gap between the workingsurfaces 38 and 40 of the top and bottom jaws 34 and 36.

The movement of the top arm 30 is restricted by the orientation of therail 70 and the guide block 74 which is connected to the flange 68.Because the guide block 74 can only move vertically as dictated by therail 70, the flange 68 and the integrally attached top arm 30 can onlymove vertically as well. The vertical motion requires the parallelangular relationship of the top and bottom jaws 34 and 36 to remainconstant as the top arm 30 opens and closes relative to the bottom arm32.

The jaws 34 and 36 are attached to the top and bottom arms 30 and 32 sothat the working surfaces 38 and 40 of the jaws 34 and 36 extendparallel with one another in a longitudinal dimension extending alongthe arms 30 and 32. The transverse dimension of the working surfaces 38and 40 may also be planar with respect to one another (FIG. 12), butpreferably one of the working surfaces has a slight convex or crownedshape (FIG. 13) while the other working surface is planar.

The parallel movement of the top and bottom arms 30 and 32 and the topand bottom jaws 34 and 36 allows the working surfaces 38 and 40 to applyand distribute force evenly across the compressed interface 46 (FIG. 4)and until the compressed tissue is separated at the parting line 51(FIG. 5). The even force application is important to obtain even anduniform reconstitution of the denatured protein chains during fusion andeven and uniform parting of the tissue along the separation line 51during cutting, all of which results in enhanced strength and integrityof the sealed interface 46 (FIG. 4) and the sealed areas 50 (FIGS. 6 and20) adjacent to the separation line 51. The parallel movement of theworking surfaces 38 and 40 does not impart any shearing force on thesealed areas 50 (FIGS. 6 and 20) as the working surfaces 38 and 40separate from one another. Such a shearing force could compromise theintegrity of the fused interface 46 (FIG. 4), apart from whether theheated, compressed and cut vessel 21 has any tendency to stick to theworking surfaces of the jaws as they separate.

The mechanical advantage resulting from closing the handles 24 and 26,transferred through the parallel movement mechanism 28, moves the arms30 and 32 and jaws 34 and 36 to compress and cut the vessel 21 uniformlyat each point on the interface 46 of the two apposite vessel walls 44.The applied force results in compressing the heated pieces of tissue toa compressed tissue thickness sufficient to fuse the tissue pieces,which in the case of blood vessels is about 0.05-0.10 mm, at which pointfusion occurs. Continued compression of the pieces of tissue until athickness of approximately zero (no gap) is achieved between the workingsurfaces results in cutting the tissue, after it has been fused. Inorder to achieve this range of compression, the parallel movementmechanism 28 must obtain an adequate mechanical advantage to transfer acomfortable amount of force applied on the handles 24 and 26 to thetissue. The force is related to the pressure between the workingsurfaces 38 and 40. The pressure is determined by the confrontationalsurface areas of the working surfaces 38 and 40 and the amount of forceapplied to the arms 30 and 32.

In a preferred embodiment, the working surfaces have a length of about25 mm and a transverse width of about 5 mm, creating an effectiveconfrontational surface area of approximately 125 mm². The mechanicaladvantage must therefore be capable of producing pressure of at least1.2 Newtons per square millimeter (N/mm²) with comfortable squeezingpressure on the handles 24 and 26. Producing a pressure of 1.2 N/mm²will assure a force of 150 N at each point of the compressed appositetissue followed by severing of the tissue as a result of the forcecreating a zero gap between the working surfaces. Producing a pressureof 0.88-1.2 N/Mm² will assure a force of 110 N-150 N at each point ofthe compressed apposite tissue before it is severed. Because thepressure may vary according to the size of tissue squeezed between theworking surfaces 38 and 40, the force applied at each point to the twopieces of compressed tissue is a measure of the effectiveness of thecompression necessary to achieve good tissue fusion and cutting.However, pressure must be considered to assure that an adequate amountof compression force is available to ultimately achieve the zero or nodistance gap between the working surfaces 38 and 40 of the jaws 34 and36 to cut the tissue following fusion.

Details of the jaws 34 and 36 are better understood by reference toFIGS. 3-5 and 8-13. Each jaw 34 and 36 is essentially of the samestructure and configuration, although the top and bottom jaws may be ofa mirror image configuration with respect to one another. Each jaw 34and 36 is preferably formed of a ceramic material with a high thermalconductivity, such as aluminum nitride. The jaws 34 and 36 are securedto the arms 30 and 32 with an adhesive, such as epoxy, which is appliedin a layer 86 between the jaws 34 and 36 and the arms 30 and 32.Insulating spacers 90 are positioned near the distal and proximal endsof each of the jaws 34 and 36 between the jaws 34 and 36 and the arms 30and 32. The adhesive layer 86 occupies the spaces between the spacers90, the jaws 34 and 36 and the arms 30 and 32.

The heating elements 49 are embedded in the ceramic material of the jaws34 and 36, as shown in FIGS. 8, 10 and 11. The heating element 49 ineach jaw 34 and 36 is essentially the same. Similarly, both jaws 34 and36 are essentially the same, except with respect to the possibility ofone or both of the jaws having a crowned working surface (FIG. 13) andthe two jaws being mirror image configurations with respect to oneanother. Because of the similarities, the heating element 49 and the jaw36 are described in conjunction with FIGS. 9-13, with the understandingthat the heating element 49 and the jaw 34 are essentially the same.

The heating element 49 is formed by a length of an electricallyconductive resistance material which produces heat when conductingelectrical current. The heating element 49 has a high thermal shockwithstanding capability and a high power density conducting capability.An example of one such electrically conductive resistance material whichoffers these capabilities is molybdenum. The heating element 49 extendssubstantially over the area of the jaw 36 (FIG. 11) so that heat isproduced relatively uniformly throughout the jaw. The heat from theheating element 49 is conducted substantially uniformly through the jaw36 due to the high thermal conductivity of the ceramic material fromwhich the jaw 36 is formed, resulting in approximately equal temperaturefrom point to point along the working surface 40 of the jaw 36.

Electrical wires 96 and 98 connect to opposite ends of the heatingelement 49. Electrical current is supplied to the heating element 49through the wires 96 and 98. The wires 96 and 98 extend throughshoulders 100 and 102 which are formed on a back side 104 of the jawfrom the same ceramic material as the jaw 36. The shoulders 100 and 102surround and support the wires 96 and 98 and hold them in position aspart of the jaw 36. The ceramic material of the jaw 36 is an electricalinsulator, thereby assuring that the current conducted through the wires96 and 98 flows through the heating element 49 without short-circuitingto the arms 30 and 32 of the instrument 22 (FIG. 1).

To embed the heating element 49 within the jaw 36, enough powderedceramic material to form the working surface 40 and the outer portion ofthe jaw 36 is placed in a mold and sintered. Thereafter, the heatingelement 49 is placed on this outer partially-formed jaw portion,preferably by using conventional fluid deposition techniques such asinking. More powdered ceramic material is then placed on top of thesintered outer portion of the jaw and the heating element 49 to form theremaining inner portion of the jaw including back side 104 and theshoulders 100 and 102. Thereafter, the powdered ceramic material whichforms the inner portion of the jaw is sintered to form the ceramic innerportion of the jaw 36 while also sintering that inner portion of the jaw36 to the previously-formed outer portion of the jaw 36, therebycompleting the integral ceramic structure of the jaw.

In addition to embedding the heating element 49 within the jaw in themanner described, the heating element can also be embedded by followingthe described procedure but without sintering the outer portion untilthe inner portion has also been formed. A single sintering occurs withrespect to both the outer and inner portions simultaneously to hold theheating element in place.

The wires 96 and 98 are mechanically and electrically connected to theends of the heating element 49 by drilling holes through the shoulders100 and 102 until the holes contact the ends of the embedded heatingelement 49. The wires 96 and 98 are inserted through the holes until theends of these wires contact the ends of the heating element 49. The endsof the wires 96 and 98 and the ends of the heating element 49 arepermanently connected together by brazing in an oven. The wires 96 and98 and the shoulders 100 and 102 therefore extend from the back side 104of the jaw 36.

When the jaws 34 and 36 are attached to the arms 30 and 32,respectively, by the adhesive layer 86, the wires 96 and 98 extendthrough openings 105 and 107 which are formed in each of the arms 30 and32 to receive the wires 96 and 98, as shown in FIGS. 8 and 10. Theopenings 105 and 107 are sufficiently large to avoid electrical contactwith the wires 96 and 98, although the wires 96 and 98 are insulated inthe areas within the openings 105 and 107. Conductors 106 and 108connect to the ends of the wires 96 and 98. The conductors 106 and 108from each jaw 34 and 36 extend through the housing 52 of the parallelmovement mechanism 28 and along the top handle 24 to the power controldevice 48, as shown in FIGS. 1 and 2. The power control device 48delivers the electrical current through the conductors 106 and 108 tothe heating element 49 in each jaw 34 and 36, thereby heating the jaws.

The current supplied by the power control device 48 (FIGS. 1 and 2) isregulated relative to the temperature of the working surfaces 38 and 40of the jaws 34 and 36. The temperature of each jaw is separatelymeasured by a thermocouple 110 associated with each jaw, shown in FIGS.3-5, 7 and 9. The thermocouple 110 associated with each jaw 34 and 36 isessentially the same. Therefore, only one thermocouple 110 is describedin association with the jaw 36 shown in FIG. 10, since the otherthermocouple is substantially identical.

The thermocouple 110 comprises an electrical node or junction 112 of twodissimilar metal wires 116 and 118, as shown in FIG. 10. The junction ofthe two dissimilar wires 116 and 118 creates a conventional type JT/Cthermocouple junction 112. A slight voltage is developed at the junction112 by the inherent electrical characteristics of the two dissimilarmetal wires 116 and 118, and the magnitude of that voltage varies inrelationship to the temperature of the junction 112. Thus, the voltagedeveloped at the junction 112 is related to the temperature of thejunction 112. The wires 116 and 118 extend through an opening 119 formedin each arm 30 and 32 (FIGS. 3-5). The wires 116 and 118 may beinsulated over that portion of their length which extends through theopening 119.

The voltage developed at the junction 112 is conducted through the wires116 and 118 to conductors 120 and 122, which connect to the ends of thewires 116 and 118, respectively. The conductors 120 and 122 extend fromthe thermocouple 110 of each jaw 34 and 36 through the housing 52 of theparallel movement mechanism 28 and along the top handle 24 to the powercontrol device 48, as shown in FIGS. 1 and 2. The voltage from thethermocouple 110, conducted through the conductors 120 and 122, is usedby the power control device 48 as a feedback signal to control theamount of electrical current delivered through the conductors 106 and108 and the wires 96 and 98 to the heating element 49 in the jaws 34 and36, thereby independently regulating the temperature of the workingsurfaces of the jaws.

The thermocouple 110 is permanently thermally and mechanically attachedto the jaw by oven brazing the junction 112 of the dissimilar metalwires 116 and 118 within a recess 114 formed into the ceramic materialon the back side 104 of each jaw, as shown in FIG. 10. The attachment ofthe junction 112 to each jaw establishes good thermal conductivity ofthe junction 112 with each jaw, thereby enabling the junction 112 torespond to the temperature of the jaw. The high thermal conductivitymaterial of each jaw distributes the heat from the heating element 49throughout the jaw relatively rapidly. The temperature of the workingsurface of the jaw is typically slightly different from the temperatureof the junction 112 because the junction 112 is not exactly at theworking surface and slight dynamic thermal gradients exist within thejaw despite the high thermal conductivity of the jaw material. However,the temperature measured by the thermocouple junction 112 is closelycorrelated to the temperature of the working surface of the jaw, toresult in temperature measurements which closely represent thetemperature of the jaw working surface. Moreover, because the tissuecompressed between the jaws during tissue fusion is relatively thin, thethermal transfer to the thin tissue causes that tissue to assume atemperature which is very close to the temperature of the jaw workingsurfaces.

Both of the working surfaces 38 and 40 may be flat and planar as shownin FIG. 12. In such circumstances the planar working surfaces aremaintained in a parallel relationship with one another by thepositioning of the jaws 34 and 36 on the arms and by the parallelmovement of the arms 30 and 32. Longitudinal edges 124 of the jaws 34and 36 are rounded or radiused to avoid imparting or concentratingpressure to the vessel 21 in such a way to weaken the vessel at the edgeof seal formed or to cut the vessel at the edge of the sealed area,thereby creating a weakened sealed area.

A preferred alternative to the planar configuration of the workingsurfaces 38 and 40 is one flat planar working surface and a crownedworking surface on the opposite jaw. Both working surfaces could also becrowned. A crowned working surface 40 is shown in FIG. 13. The workingsurface 40 possesses a slight outward convex shape when viewedtransversely to the longitudinal dimension of the jaw 36, as shown inFIG. 13. The crowned or convex curvature of the working surface isuseful for applying more force to the vessel at the center of theworking surface for cutting the sealed area, while simultaneouslycreating a slightly graduated variation in the extent of tissuecompression from the center of the working surface to the longitudinalradiused edges 124. The slight variation in compression is instrumentalin achieving separation of tissue along the separation line 51 (FIGS. 6and 20) while simultaneously achieving an optimal sealing force on thetissue squeezed between the working surfaces 38 and 40. However, in mostcases, once adequate pressure is obtained, it is not necessary toachieve optimal pressure to accomplish adequate fusion with the presentinvention, so long as sufficient force is ultimately applied to reducethe thickness of compressed tissue to zero between the working surfacesalong the separation line 51 at the fused area.

The curvature of the crowned working surface 40 of the jaw is in thetransverse direction across the working surface. The amount of curvatureof the working surface 40, as shown in FIG. 13, is such that the radiusof curvature of the working surface 40 in the transverse dimension isapproximately 21 mm at a point where the transverse width of the jaw isapproximately 5 mm. This radius of curvature generally causes the centerof the crowned working surface to be approximately 0.1 mm higher thanthe working surfaces near the longitudinal edges 124 of the 5 mm widejaw 36, before those longitudinal edges 124 are radiused.

Each of the jaws 34 and 36 also curves laterally to the side, in thegeneral shape of the typical “Maryland” jaw shape which is frequentlypreferred by surgeons, as shown in FIGS. 1, 2, 6-9 and 11. Furthermorethe most forward or distal end of each of the jaws 34 and 36 has areduced transverse dimension compared to the transverse dimension of theproximal or rearward end. This “Maryland” jaw shape facilitates viewingthe jaws monoscopically during minimally invasive surgery, and thelesser transverse dimension of the distal end is useful for bluntdissection. The point of maximum convex curvature of the crowned workingsurfaces of such “Maryland” jaws extends on a curve which isapproximately equidistant transverse between the edges of the jaws.Cutting occurs along the curved array of linear points of maximum convexcurvature, and it is through the curved shape of the jaws thatelectrothermal cutting is accomplished on a linear curve. The curvedcutting is reflected in the curvature of the separation line 51.

An important aspect of the present invention is that the workingsurfaces 38 and 40, and preferably side surfaces 123 and 125 (FIGS. 9,12 and 13) and the radiused longitudinal edges 124 of the jaws 34 and36, have a high degree of smoothness. A sufficiently high degree ofsmoothness is capable of preventing any sticking of the compressed andheated tissue to the jaws 34 and 36 after the vessel 21 has been sealedand cut. The smoothness of the side surfaces 123 in 125 similarlyprevents any overhanging tissue adjacent to the working surfaces 38 and40 from sticking to the jaws 34 and 36 when the vessel 21 is sealed andcut. Eliminating the occurrence of tissue sticking to the jaws is asubstantial improvement because sticking tissue is responsible fordestroying or substantially weakening the seal in a significantproportion of those incidents where the seal fails. Eliminating theoccurrence of tissue sticking to the jaws also offers a substantialconvenience to surgeons, because a considerable amount of time isconsumed during the surgical procedure in cleaning the jaws of adheredtissue. By avoiding the necessity to clean the jaws, a time required toperform the surgical procedure is diminished, resulting in reduced riskand trauma to the patient.

The conventional measurement of smoothness is referred to as Ra. Toachieve the degree of smoothness most desirable in accordance with thepresent invention, the working surfaces 38 and 40, the side surfaces 123and 125 and the longitudinally radiused edges 124 of the jaws 34 and 36,are formed from a ceramic material, such as aluminum nitride, or amaterial having a surface microstructure like ceramic material, and suchsurfaces have an Ra of 0.15 microns or less. Jaws formed of aluminumnitride with surfaces having a smoothness represented by an Ra of 0.15microns or less have been determined to result in no tissue sticking tothe jaws after fusion and cut procedure has been completed and the jawsare separated.

For jaw surface smoothness in the Ra range of 0.15 to 0.40 microns, aspectrum of smoothness exists where the frequency of sticking increasesin relation to decreasing smoothness, although the frequency of stickingis not in a linear relationship to decreasing smoothness. For a smallincrease in smoothness at the lower end of the range, a large reductionin the frequency of tissue sticking occurs. For an Ra of 0.15 microns orless, no sticking of the tissue has been observed, and the forcerequired to separate the working surfaces from the vessel is notsignificantly different than if the vessel had not been present betweenthe working surfaces. For an Ra range of 0.15 to 0.20 microns, stickingdoes not occur or only occurs with very minimal or virtually nonexistentfrequency, and the force required to separate the working surfaces fromthe sealed and cut vessel is not significantly greater than the forcerequired to separate the working surfaces from the sealed and cut vesselwhen the Ra is less than 0.15 microns. In the Ra range of 0.20 to 0.25microns, sticking occurs with a slightly greater frequency, and theforce required to separate the tissue from the working surfaces isslightly increased. In the Ra range of 0.25 to 0.40 microns, a moderateincrease in the frequency of sticking occurs, and the force required toseparate the tissue from the working surfaces is also moderatelyincreased. Finally, in the Ra range of 0.40 to 0.50 microns, stickingbecomes significantly more frequent and the force required to separatethe tissue from the working surfaces is further increased. However, anRa in the range of 0.40 to 0.50 microns provides less tissue stickingthan with the known prior art jaws used for tissue fusion by itself, ortissue fusion and simultaneous cutting, or for those jaws which have anRa of about 0.60 microns or greater.

The sticking of tissue described herein applies to that tissue uponwhich pressure has been applied from the working surfaces during tissuefusion and cutting. Sticking is not intended to apply to any tissue orfluid, such as blood, which remains on the working surfaces after thejaws have been separated and the sealed and cut tissue is removed fromthe working surfaces. Although tissue and fluid may remain on theworking surfaces after the tissue is removed, such tissue and driedfluid may easily be wiped from the working surfaces.

A conventional profilometer is used to measure the roughness of theworking surfaces and to obtain the Ra values described herein. Oneexample of such a commercially available profilometer is a Pocket Surf®portable surface roughness gauge manufactured by Mahr Federal, Inc. ofGermany. Prior to measuring the roughness of the working surfaces, theprofilometer was calibrated using a reference that had a known Ra. TheRa reference was certified against a known standard in accordance withISO or ANSI standard procedures. The exemplary profilometer employed toobtain the Ra measurements described herein had an accuracy of ±0.05microns and a resolution of 0.01 microns.

One useful ceramic material from which to form the jaws 34 and 36 isaluminum nitride. Aluminum nitride has a relatively high thermalconductivity of about 140-180 W/m ° K. Aluminum nitride can also bepolished to a smoothness of an Ra of 0.15 microns or less. When removedfrom the sintering oven after formation in a smooth mold, aluminumnitride can have an Ra as low as 0.60 microns, but not significantlylower. Working surfaces with an Ra of 0.60 microns appear smooth, butthat apparent smoothness is above the acceptable range of Ra inaccordance with the present invention.

Any polishing or other smoothing technique that can achieve the desireddegree of smoothness of the working surfaces may be employed inaccordance with the present invention. A satisfactory level ofsmoothness of the working surfaces of aluminum nitride jaws has beenachieved by polishing the working surfaces using various grits ofdiamond paper or diamond pastes. Finer grades of abrasives were used insuccession as the polishing proceeded toward the desired smoothness. Thedesired degree of smoothness was achieved by polishing the workingsurfaces by hand, successively using diamond grit paper with particlesizes of 6, 3, 1, 0.50, 0.25 and 0.10 microns in that order.

If the polishing is initiated with a grinding wheel or grit paper havinga too coarse particle size, the working surface may be damaged androughened to the extent that the desired smoothness can not be achievedwhen finer grits are used subsequently in the polishing process. Whenstarting the polishing with too coarse of a particle size, the highestdegree of smoothness (Ra of 0.15 microns or less) is difficult orimpossible to achieve on aluminum nitride ceramic surfaces.

A strictly uniform smoothness across the working surfaces 38 and 40 isnot required. Only those portions of the working surfaces 38 and 40which contact the vessel 21 (FIG. 2) must be smoothed to the desireddegree to obtain reduced tissue sticking. Thus, to the extent that theside surfaces 123 and 125 do not touch tissue, they may not require thesame degree of smoothness as the working surfaces 38 and 40 and thelongitudinal radiused edges 124.

The amount of force transferred from the working surfaces 38 and 40 ofthe jaws 34 and 36 to the vessel 21 is measured by a conventional straingauge 126 attached to a section 128 of the top proximal handle 24, shownin FIG. 7. The section 128 of the top handle 24 has a reducedcross-sectional area. The strain gauge 126 is attached to extendlongitudinally along the reduced cross-sectional area section 128.Attached in this manner, the strain gauge 126 measures the amount ofdeflection of the section 128 created by the force resulting fromsqueezing the handles 24 and 26 together. The extent of deflection ofthe section 128 is accurately correlated to the amount of force appliedfrom the distal arms 30 and 32 to the tissue squeezed between theworking surfaces 38 and 40 (FIG. 4) and as the tissue separates when thedistance between the working surfaces 38 and 40 approaches zero (FIG.5). The signals from the strain gauge 126 are conducted through twoconductors, collectively referenced 130, to the power control device 48,where those force-related signals are used to create a display of theforce imparted to the compressed tissue and to control the power controldevice 48.

A handle locking and release mechanism 131 is connected to the proximalends of the handles 24 and 26, as shown mainly in FIG. 7, and also inFIGS. 1, 2 and 6. The handle locking and release mechanism 131 includesa curved extension 132 with ratchet teeth 134 that extends downward fromthe proximal end of the top handle 24. The bottom handle 26 includes aratchet pawl 136 that extends rearward from the proximal end of thebottom handle 26. The ratchet pawl 136 is connected to a rod 138 whichextends longitudinally within the interior of the bottom handle 26. Aspring 140 is connected between a proximal end of the rod 138 and ashoulder 141 of the bottom handle 26. The spring 140 is compressed andnormally biases the rod 138 in the rearward direction. The normalrearward bias from the spring 140 on the rod 138 extends the ratchetpawl 136 rearward from the proximal end of the bottom handle 26.

When the handles 24 and 26 are squeezed together, the ratchet pawl 136slides by and engages the individual ratchet teeth 134 in succession,until the handles 24 and 26 reach a squeezed-together position where thedesired amount of force is applied on the compressed vessel 21. Thehandles can not separate or open because the ratchet pawl 136 is engagedwith the ratchet teeth 134, thereby allowing the working surfaces 38 and40 to maintain force on the compressed vessel 21 during fusion. Thehandle locking and release mechanism 131 allows an adequate andsubstantial amount of force or pressure to be maintained on the vessel21 during fusion without requiring the surgeon to continually squeezethe handles 24 and 26. The handle locking and release mechanism 131 alsoprevents the force or pressure on the compressed vessel fromsubstantially decreasing during the tissue fusion and simultaneouscutting procedure. The interaction of the ratchet pawl 136 with theratchet teeth 134 prevents the handles 24 and 26 from moving apart fromtheir squeezed-together position, until the ratchet pawl 136 isseparated from the ratchet teeth 134.

The handle locking and release mechanism 131 includes a trigger 142which, when squeezed, separates the ratchet pawl 136 from the ratchetteeth 134 and thereby allows the handles 24 and 26 to open with respectto one another. The trigger 142 includes a contact arm 144 whichcontacts and interacts with a shoulder 146 at the distal end of the rod138. The normal bias from the spring 140 on the rod 138 biases theshoulder 146 against the contact arm 144, and causes the trigger 142 toassume the normal position shown in FIG. 2, with a release arm 148 ofthe trigger 142 extending generally parallel with the elongateddimension of the bottom handle 26. To disengage the ratchet pawl 136from the ratchet teeth 134, the trigger 142 is squeezed which causes therelease arm 148 to pivot counterclockwise as shown in FIG. 7. Thecounterclockwise movement of the contact arm 144 against the shoulder146 moves the rod 138 in the distal direction, as shown in FIG. 7, andthe distal movement of the rod 136 releases the engagement of theratchet pawl 136 with the ratchet teeth 134. With the ratchet pawl 136released from the ratchet teeth 134, the handles 24 and 26 are free tomove away from one another.

The following example illustrates the utility of the smooth workingsurfaces 38 and 40 in tissue fusion and simultaneous cutting. In twoseparate laboratory experiments, tissue fusion and simultaneous cuttingwas performed on mesentery and spleen tissue. The tissue fusion andcutting instrument used in the experiment had aluminum nitride jawswhich had been hand polished to an Ra of about 0.15 microns asdetermined by at least five measurements over the working surfaces. Thealuminum nitride ceramic jaws had a width dimension of 5 mm and a lengthdimension of 25 mm and a thickness dimension of 1.5 mm. One of theworking surfaces was crowned (FIG. 13) and the other working surface wasflat or planar (FIG. 12). Each sample of tissue was compressed betweenthe jaw working surfaces with a force sufficient to reduce the gapbetween the working surfaces to zero at the conclusion of the procedure,thereby cutting the tissue. An impulse of power having a power densityof 1500 W/in2 (233 W/cm2) was delivered by the power control device 48(FIG. 1) to the heating elements in the jaws. The power impulse used infusing and simultaneous cutting the mesentery had a 2.0 second timeduration. The power impulse used in fusing and simultaneously cuttingthe spleen had a 1.5 second time duration. The power impulses producedin both instances contained enough thermal energy to successfully sealthe tissue as well as simultaneously cut the tissue. The thermocouplesof the jaws recorded peak temperatures of the jaw working surfaces ofabout 230° C. when fusing and simultaneously cutting the mesentery andrecorded peak temperatures of the jaw working surfaces of about 240° C.when fusing and simultaneously cutting the spleen.

When cutting the mesentery, 5 consecutive cuts were performed for atotal length of the cut of approximately 125 mm. The total time requiredto cut the entire 125 mm length was approximately 38 seconds. Followingthe mesentery cut procedure, a blue sheet was placed underneath the cutportion of the mesentery and the mesenteric vessels were inspected forbleeding. No bleeding was observed. When cutting the spleen, 5consecutive cuts were performed on previously unaffected live tissue,with no adverse bleeding from the sealed areas adjoining the separationline. Eleven other cuts were performed at locations which overlap areaswhich had previously only been sealed. In other words, the 11 cuts werea second procedure performed on top of an area which had previously beensealed only without cutting. Again, under such circumstances, no adverseconsequences or deterioration of the sealed areas was observed.

After each fusion and simultaneous cut procedure was performed, the jawswere separated to release the fused and cut tissue. The tissue wasconsidered stuck to one of the working surfaces if the fused and cuttissue did not separate itself immediately from the working surfacewhich contacted the tissue. Of the tissue samples which were fused andsimultaneously cut in these experiments, none adhered to the workingsurfaces of the jaws using this sticking evaluation criteria. Moreover,on occasion, blood or other tissue was present on the working surfacesof the jaws before the tissue sample was compressed between the jaws.Even in these adverse situations, the tissue did not stick to the smoothworking surfaces. The blood or other tissue initially present on thejaws adhered to the tissue sample which had been fused andsimultaneously cut, thereby producing clean working surfaces, but therewas no adherence between the fused and cut tissue and the smooth workingsurfaces. Use of the present invention subsequent to these experimentshas also confirmed the non-stick performance of the polished workingsurfaces.

More details concerning the power control device 48 are shown in FIGS.14-15. As shown in FIG. 14, the power control device 48 includes acontroller 150 which includes a memory 152 and a processor 154. Thememory 152 stores data and information supplied by conventional inputdevices 156 and/or supplied from a touch screen (not shown) of aconventional monitor 158. The information stored in the memory 152includes criteria 160 which establish the parameters for one or morestandard tissue fusion and simultaneous cutting procedures. The standardprocedure criteria 160 includes information describing the temperatureto be attained at the working surfaces 38 and 40 of the jaws 34 and 36of the instrument 22, the amount of force to be applied by the jaws 34and 36 to the vessel 21 or other tissue during the procedure, and theamount of time during which electrical power is to be delivered to heatthe jaws 34 and 36 to perform the procedure.

In addition, the memory 152 stores certain user-selected criteria 162which can be used in place of some or all the standard procedurecriteria 160 to accomplish tissue fusion and simultaneous cutting. Theability to select and alter the criteria 162 allows the user to adjustthe fusion criteria to the surgeon's preferences or to performprocedures which may be better accomplished by using user-selectedcriteria rather than standard criteria.

The memory 152 also stores the instructional code which defines certainfunctional routines 164. The functional routines 164 cause the processor154 to control the power delivered to the jaws 34 and 36. The functionalroutines 164 also contain control constants and gain factors that areused when the processor 164 executes certain functional routines, asillustrated by the examples described below.

One of the functional routines executed by the processor 154 is atemperature control feedback routine 166. The temperature controlfeedback routine 166 is executed in response to temperature signals 168and 170 obtained from the sensing of the temperatures of the top jaw 34and the bottom jaw 36 by their respective thermocouples 110 (FIG. 10)and supplied over the conductors 120 and 122. The processor 154 respondsto the individual temperature signals 168 and 170 from each of the topand bottom jaws 34 and 36 and separately regulates the amount ofelectrical power supplied to each top and bottom jaw heating element 49.In doing so, the processor 154 executes the same temperature controlfeedback routine 166 for each jaw 34 and 36, thereby separatelyregulating the temperature of each jaw 34 and 36. In most cases, it isdesired that the temperatures of both jaws 34 and 36 be the same duringthe procedure, but different amounts of electrical power may be requiredto cause each jaw 34 and 36 to attain and maintain the desiredtemperature, due to different thermal loads imposed by differentphysiology of the tissue or vessel 21 contacted by each jaw 34 and 36.

The processor 154 creates switching signals 172 and 174 which aresupplied to conventional controllable switches 176 and 178, such assolid-state relays. In response to the switching signals 172 and 174,the controllable switches 176 and 178 conduct electrical power from aconventional adjustable low-voltage, high-current direct current (DC)power supply 180 to the heating element 49 of the top jaw 34 and to theheating element 49 of the bottom jaw 36.

By separately controlling the characteristics of the switching signals172 and 174, the conductivity characteristics of the controllableswitches 176 and 178 are also separately varied to separately controlthe amount of electrical power delivered to each heating element 49 ofthe top and bottom jaws over the conductors 106 and 108. In this manner,the amount of electrical power, and consequently heat available at eachof the jaws 34 and 36, is varied independently in each jaw.

The processor 154 also executes a criteria comparison routine 184. Thecriteria comparison routine 184 utilizes the temperature signals 168 and170 from the top and bottom jaws and a force signal 186 supplied overthe conductors 130 from the strain gauge 126, as well as internallygenerated time duration information which is measured from the time thatthe impulse of electrical power is applied to the jaws 34 and 36.Execution of the comparison routine 184 creates information which ispresented on the monitor 158 as graphs or other presentations of thetemperature signals 168 and 170, the force signal 186 and the elapsedtime. The temperature of each jaw 34 and 36 may be displayed separatelyon the monitor 158, while the force and the time are presentedsingularly with respect to each separate fusion procedure.

Execution of the comparison routine 184 also compares the temperaturesignals 168 and 170, the force signal 186 and the elapsed time tocorresponding limits or values of the temperature, force and elapsedtime established by the standard procedure criteria 160 or by theuser-selected criteria 162 for the tissue fusion and simultaneouscutting procedure. The result of comparing the actual temperatures,force and elapsed time to the procedure criteria limits or values isinformation which is supplied to the monitor 158 and/or an annunciator188. Execution of the comparison routine 184 identifies if and when theactual operative values associated with the tissue fusion andsimultaneous cutting procedure fall outside of the procedure criterialimits or values. Under circumstances where the actual operative valuesachieve or deviate from the established procedure criteria values,visual and/or audible signals are delivered from the annunciator 188,and related signals may also be presented visually on the monitor 158.

For example, execution of the comparison routine 184 establishes thetime instant at which electrical power impulse is delivered to the jawheating elements. The comparison routine 184 monitors the force signal186 to determine when the vessel 21 has been compressed sufficiently toapply the electrical power impulse for heating the jaws 34 and 36. Acertain force limit must be exceeded by squeezing the handles 24 and 26before the controller 150 recognizes that a tissue fusion andsimultaneous cutting procedure is underway. Once the initial force limitvalue is attained, the controller 150 delivers the control signals 172and 174 to the controllable switches 176 and 178 to apply electricalpower to the heating element 49 of the top and bottom jaws, therebyheating the working surfaces of the jaws 34 and 36. Simultaneously, thecomparison routine 184 begins timing the time duration at which theelectrical power is delivered at the selected temperature for theprocedure.

As another example of the execution of the comparison routine 184, onceit is recognized that the temperature of the working surfaces 38 and 40of the jaws 34 and 36 has reached the selected temperature, a signal isdelivered from the annunciator 188. Under circumstances where one orboth of the top and bottom jaw temperatures exceed or fall below thetemperature limits, or under circumstances where the force between thejaws 34 and 36 has not reached the desired final level or exceeds orfalls below the desired final level, an out-of-criteria signal isdelivered from the annunciator 188. Such limit information may also bepresented on the monitor 158 as well, and is used by the surgeon duringuse of the instrument 22.

A temperature feedback power control routine 166, which offers thewell-known and significant advantage of predictive capability, is aproportional, integral, derivative (PID) computation, represented infunctional block diagram form shown in FIG. 15 by a temperature controlfeedback circuit 190. The PID temperature control feedback circuit 190is shown as interconnected individual functional devices, but the PIDfunctionality represented by the circuit 190 may also be executed by theinstructional code executed by the processor 154 of the controller 150(FIG. 14).

The temperature signal 168 or 170 supplied by the top or bottomthermocouple 110 of jaw 34 or 36 (FIG. 15) is multiplied in an amplifier192 by a scaling factor Kj which converts the value of the temperaturesignal 168 or 170 from the jaw itself to a scaled temperature signal194. The scale temperature signal 194 represents the temperature of theworking surface of the jaw. The application of heat to the jaw from theheating element 49 (FIG. 11) causes slightly different temperatures atdifferent locations in the jaws. A slight temperature gradient withinthe jaws causes the temperature at the working surfaces to be differentfrom the temperature at other locations within the jaws, including thetemperature at the location which is sensed by the thermocouple 110,despite the fact that the jaws are made from high thermal conductivitymaterial. Accordingly, the temperature sensed by the thermocouple is nottypically equal to the temperature of the working surface of the jawwhich contacts the vessel being sealed. The scaling factor Kj is used toconvert the actual thermocouple-sensed temperature signal 168 or 170 tothe scaled temperature signal 194, by multiplying the scaling factor Kjand the actual thermocouple-sensed temperature signal 168 or 170. Theresult is that the scaled temperature signal 194 closely approximatesthe actual temperature of the working surface of the jaw.

The value of the scaling factor Kj is developed empirically, underconditions where the walls 44 of the vessel 21 are contacted andsqueezed between the jaws. To empirically develop the value of Kj, it isnecessary to conduct an actual temperature measurement of the jawworking surface, which can be accomplished by using conventionalinfrared temperature measurement techniques, for example. The actualtemperature measurement is then related to the temperature measurementfrom the thermocouple to obtain the scaling factor Kj.

The scaling factor Kj may be different depending upon the desiredtemperature of the working surface of the jaw during the procedure. Forexample, the selection of a lower working surface temperature for thetissue fusion and simultaneous cutting procedure may result in a lowervalue for the scaling factor Kj compared to the scaling factorapplicable when a higher working surface temperature is selected for adifferent tissue fusion and simultaneous cutting procedure. The valuesof the scaling factor Kj are stored in the memory 52 as part of thestandard procedure criteria 160 (FIG. 14).

The amplifier 192 supplies a scaled temperature signal 194 to a negativeinput terminal of a comparator 196. A set temperature signal 198 issupplied to the positive input terminal of the comparator 196. The settemperature signal 196 represents the desired temperature of the workingsurfaces of the jaws which is to be attained and maintained during thetissue fusion and simultaneous cutting procedure. The set temperaturesignal 196 is one of the standard temperature criteria 160 or theuser-selected temperature criteria 162 stored in the memory 152 (FIG.14).

The comparator 196 subtracts the scaled temperature signal 194 from theset temperature signal 198, and the result is an error signal 200. Theerror signal 200 represents the difference between the actualtemperature of the working surfaces of the jaw (signal 194) and thedesired or set temperature of the working surfaces of the jaws for theprocedure (signal 198). It is the error signal 200 and the elapsed timethat cause the predictive aspects of the proportional, integral andderivative functionality to create a control error signal 202 which willbe used by the processor 154 to create the switching control signals 172and 174 (FIG. 14). The switching control signals 172 and 174 regulatethe temperature of the working surfaces 38 and 40 of the jaws 34 and 36.

The proportional aspect of the PID functionality is achieved bymultiplying the error signal 200 by a proportional constant Kp in anamplifier 204. A proportionalized error signal 206 is created by theamplifier 204 and is supplied to one input terminal of a summer 208. Thevalue of the proportional constant Kp is established through selectionof the standard criteria 160 or the user-selected criteria 162 stored inthe memory 152 (FIG. 14).

The integral aspect of the PID functionality is achieved by integratingthe error signal 200 in an integrator 210. The integrator 210 suppliesan integrated error signal 212 which is then multiplied in an amplifier214 by an integration constant Ki to create an adjusted integrated errorsignal 216. The adjusted integrated error signal 216 is applied toanother input terminal of the summer 208. The value of the integrationconstant Ki is established through selection of the standard criteria160 or the user-selected criteria 162 stored in the memory 152 (FIG.14).

The differential aspect of the PID functionality is achieved bydifferentiating the error signal 200 in a differentiator 218 to create adifferentiated error signal 220. The differentiated error signal 220 isthen multiplied in an amplifier 222 by a differentiation constant Kd tocreate an adjusted differentiated error signal 224. The differentiatederror signal 224 is applied to a third input terminal of the summer 208.The value of the differentiation constant Kd is established throughselection of the standard criteria 160 or the user-selected criteria 162stored in the memory 152 (FIG. 14).

Although the differentiator 218 is shown as receiving the error signal200, it is also possible for the differentiator 218 to respond to thescaled temperature signal 194. Under such circumstances, thedifferentiation of the scaled temperature signal 194 results in a highervalue of the signal 220. Under these circumstances the value of thedifferentiation constant Kd is adjusted to represent the changed valueof the signal 220.

The proportionalized error signal 206, the adjusted integrated errorsignal 216 and the adjusted differentiated error signal 224 are summedtogether in the summer 208. The result of the addition is the controlerror signal 202. The values of the proportional constant Kp, theintegration constant Ki and the differentiation constant Kd are allselected to achieve the desired predictive capability resulting from thecontribution of the proportionalized, integrated and differentiatederror signals 206, 212 and 220 in creating the control error signal 202.Adjusting the values of the PID constants Kp, Ki and Kp in this mannerallows the error signal 202 to achieve the desired degree of control toheat the jaws.

The values of the proportional constant Kp, the integration constant Kiand the differentiation constant Kd are different based upon the desiredset temperature and the time for the fusion procedure. The amount offorce applied during the fusion procedure may also have an effect on thevalue of the PID constants Kp, Ki and Kd, although that impact willgenerally be less than the effect from the desired temperature and timeduration of the fusion procedure.

The values of the PID constants Kp, Ki and Kd may remain constantthroughout the delivery of power during the course of a singleprocedure, or they may also be varied during the delivery of power in asingle procedure. For example one set of PID constants may be used whenincreasing the temperature of the working surfaces of the jaws to thedesired set temperature, and another set of PID constants may be used tomaintain the temperature of the working surfaces at the desired settemperature during the tissue fusion and simultaneous cutting procedure.The criteria comparison routine 184 executed by the processor 154 (FIG.15) substitutes the different proportional constants into thetemperature control feedback routine 166 and the temperature controlfeedback circuit 190 according to the temperature of the jaw workingsurfaces, the elapsed time of the power impulse, and to a lesser degree,the force applied. All of the values of the PID constants are stored inthe memory 152 (FIG. 14).

In response to the control error signal 202, the power control device48, shown in FIGS. 14 and 15, delivers an impulse of electrical powerwhich is sufficient to raise the temperature of the working surfaces ofthe jaws from room temperature to a sealing set point temperature ofabout 220° C. to 320° C. at a rate greater than 150° C. per second andpreferably greater than 500° C. per second. The rate should be as highas possible without creating untoward side effects on the tissue. Ofcourse, the power control device 48 also has the capability ofmaintaining the selected temperature for the time duration of the powerimpulse, which is preferably about 1.5 to 2.0 seconds but which mayextend to approximately 4.0 seconds. In general, the impulse of powerbegins with the switching signals 172 and 174 causing the controllableswitches 176 and 178 to deliver DC current from the power supply 180until the temperature of the jaws approaches the set point temperature.Thereafter the switches 176 and 178 are turned on and off to maintainthe set point temperature during the fusion procedure. In general theon-time decreases and the off time increases to maintain the set pointtemperature after it is initially achieved. Delivering the impulse ofpower is effective to quickly establish and maintain a set pointtemperature creates a strong and effective seal while simultaneouslycutting the tissue.

To achieve these temperatures, a power density of about at least 1500W/in2 (2.33 W/mm²) and preferably greater than 2500 W/in2 (3.88 W/mm²)is typically required, with the usual power density being in the rangeof 2500 W/in2 to 3000 W/in2 (3.878 W/mm² to 4.64 W/mm²). Higher powerdensities are required to achieve shorter procedure times and to sealand simultaneously cut larger vessels and more massive tissues. However,the power density is not always an accurate representation of thecapability of raising and maintaining the working surfaces of the jawsat the desired tissue fusion temperature. The thermal load created bythe compressed vessel or tissue is variable, and thus directlyinfluences the power density. Moreover, the distal arms 30 and 32 of theinstrument 22 (FIG. 1), the wires 96 and 98 and the conductors 106 and108 connected to the jaw heating elements 49 (FIG. 13) and thedissimilar wires 116 and 118 of the thermocouple 110 and conductors 120and 122 connected to the thermocouples 110 (FIG. 8) act as heat sinks totransfer thermal energy away from the jaws, thereby making it difficultto account accurately for the amount of energy delivered to the vessel21 and that amount of energy dissipated to the instrument 22. As aconsequence, the temperature of the working surfaces of the jaws is abetter indication of the important thermal variable for fusing tissue.

The temperatures of the working surfaces 38 and 40 must be sufficientlyhigh to denature the collagen fibers at a temperature of about 60-70° C.and also high enough to denature the elastin fibers at a temperature ofabout 120° C., and to quickly obtain enough dehydration of thecompressed tissue to achieve good reconstitution of the denatureproteins chains and to maintain some resiliency or pliability of thesealed tissue while the cut occurs, all before the tissue becomes toodehydrated to permit good fusion. By delivering an impulse of power thatcan heat the working surfaces of the jaws to temperatures in the rangeof 220° C. to 320° C. and maintaining that temperature for a preferabletime duration of about 1.5 to 2.0 seconds while the vessel is compressedfor sealing and thereafter simultaneously cut, the collagen and elastinfibers are first denatured and then reconstituted across the interface46 to create a strong seal and then the heat continues to force thesealed area to separate along the separation line 51 (FIG. 1).

Because the electrical power is delivered for a short period of time,the heat generated by this power does not diffuse appreciably into thesurrounding walls of the vessel. As a result, the walls adjacent to theseal remain substantially unaffected by thermal energy spread. Thestrength and capability of the adjacent tissue is not compromised to thepoint where it may contribute to a failure of the seal.

Sealing a vessel with an impulse of electrical power which elevates thetemperature of the working surfaces to a set temperature ofapproximately 220° C. and maintains that 220° C. sealing andsimultaneous cutting temperature for a time of about 2.0 seconds isillustrated by the graph shown in FIG. 16. The temperature of theworking surface on the upper jaw is referenced at 226, and thetemperature of the working surface of the lower jaw is illustrated at228. The temperatures in the upper and lower jaws are comparable to oneanother, due to the independent and rapid temperature control feedbackof the controller 150 (FIG. 14).

The electrical power is applied by the controller to the jaw heatingelements beginning at the 0.0 time reference. The energy applied for aninitial ramp up time increases the temperature of the working surfacesfor approximately 0.7 seconds, at which time the temperature of the jawworking surfaces is approximately at the desired 220° C. set pointtemperature for the tissue fusion procedure. Thereafter, betweenapproximately 0.7 seconds and 2.0 seconds, the controller 150 managesthe delivery of electrical power to maintain the temperature of the jawworking surfaces at the set point temperature of about 220° C. A slightamount of temperature overshoot and undershoot occurs immediately afterthe transition from the initial temperature ramp-up to the desired setpoint temperature, but that slight oscillation of temperature is withinan acceptable range of the desired set point temperature.

After the delivery of power is stopped at 2.0 seconds, the impulse ofelectrical power is terminated and the jaws are opened immediatelythereafter to release the severed vessel. The annunciator 188 or themonitor 158 (FIG. 14) indicates when the jaws can be opened to releasethe severed vessel. After the vessel is released from the jaws, thesealed areas 50 (FIGS. 6 and 20), which are adjacent to the separationline 51, lack substantial mass to retain heat and cool rapidly whenexposed to air. The jaws also quickly cool in the air after release ofthe tissue, but that cooling is not material to the invention and istherefore not shown in FIG. 16.

Sealing a vessel with a 1.5 second impulse of power which achieves a jawworking surface temperature of approximately 320° C. is illustrated inFIG. 17. Each of the top and bottom jaw working surface temperatures areseparately referenced at 230 and 232. The temperature rapidly increasesfrom 0.0 seconds to the set temperature of about 320° C. in slightlymore than 0.5 seconds. Thereafter, the delivery of electrical power tothe jaw heating elements is controlled to maintain the working surfacetemperature at about 320° C. until 1.5 seconds have elapsed since thecommencement of delivering the electrical power impulse. At that time,the electrical impulse is terminated and the jaws are opened to releasethe vessel. Again, the sealed areas, which are adjacent to theseparation line 51, cool rapidly upon being exposed to the air. The jawsalso quickly cool in the air after release of the tissue, but thatcooling is not material to the invention and is therefore not shown inFIG. 17.

At temperatures of 220° C. to 320° C., the time duration of the powerimpulse must be relatively short to avoid damaging, destroying orsubstantially weakening the vessel. For example, maintaining thetemperature of approximately 320° C. for 5.0 seconds has the effect ofso dehydrating the tissue between the working surfaces of the jaws sothat it becomes friable and brittle. Such characteristics make thesealed areas prone to break or crack and develop a leak and cause theseparation at the sealed areas of the vessel to break or crack along anill-defined and nonlinear path.

The staircase nature of the curves 226, 228, 230, and 232 shown in FIGS.16 and 17 result from a digital sampling routine of the PID controller.The discrete sampling points observed in FIGS. 16 and 17 are separatedby significant amounts of time, but higher sampling frequencies arepossible. Increasing the rate of sampling by the PID controller allowsfor better system control over such variables as overshoot and risetime.

The strength and integrity of the seals adjacent to the separation line51 (FIGS. 6 and 20) created by use of the present invention have beenevaluated using burst tests. To evaluate the strength of the seal with aburst test, the lumen of the vessel is connected to a source ofpressurized fluid, such as air, which inflates the vessel adjacent tothe sealed area until a rupture or burst in the sealed area or thevessel wall occurs. The fluid pressure at the rupture point is measured,and the rupture pressure represents the strength of the seal. The testis repeated many times with different specimens of sealed tissue. Asufficient number of burst tests are conducted to achieve astatistically significant number of samples by which to evaluate thestrength and integrity of the seals. The burst tests indicate that theseals formed have some range of variability in strength, and the sealstrength is dependent upon the type and the size of the vessel sealed.Despite the variations in the seal strength, the burst pressuresobserved indicate that the seals formed have more than sufficientstrength to reliably withstand the applicable physiological pressures,and in most cases, multiples of those pressures.

In addition to having a statistically higher and more consistent burstpressure, the typical failure mode of a seal made in accordance with thepresent invention is also substantially different from the edge-sealleak or mid-seal wall leak failure modes of seals made by use of thetypical, known prior art tissue fusion devices which are presently insignificant use. Typical edge-seal or mid-seal wall leaks areillustrated in FIGS. 17 and 18, respectively.

As shown in FIG. 18, a vessel 234 has been sealed at area 236 by atypical prior art technique. The view of FIG. 18 is orthogonal to therelatively large flat surface of the sealed area 236. An edge 238 of thesealed area 236 delineates its boundary. An edge-seal leak occurs atlocation 240 when the edge 238 of the sealed area 236 ruptures through awall 242 of the vessel 234 at a location adjacent to the sealed area236, under the influence of pressure applied in the lumen 244 on theleft-hand side of the vessel (as shown). Usually the edge-seal leak 240results from the application of excessive heat and compressionconcentrated at the edge 238 or over the entire sealed area 236, or as aresult of RF arcing which impacts the wall 242 of the vessel 234 andweakens the vessel at or near the edge 238. The edge 238 may also beweakened by excessive compression from non-parallel jaws of a handpieceor from a 20 shearing action on the tissue at the sealed area whenseparating the jaws, as described above. The edge-seal leak 240 divertsfluid from the lumen 244 to the outside of the vessel 234.

The typical mid-seal wall leak is illustrated in FIG. 19 where a vessel246 was previously sealed at an area 248 by a typical prior arttechnique. The view of FIG. 19 is parallel to the flat surfaces of thesealed area 248. The sealed area 248 was formed by compressing andfusing apposite walls 250 of the vessel 246. Unsealed vessel walls 250extend away from edges of the sealed area 248. Under the influence ofpressure applied in the lumen 252 on the left-hand side of the vessel246 shown in FIG. 19, the sealed wall portions of the sealed area 248have started to separate due to the fluid pressure against the sealedarea 248. A remaining portion 254 of the sealed area 248 remains intactwith the walls of the vessel sealed together. A mid-seal wall leak 256occurs when the separated vessel wall of the previously sealed area 248ruptures at 256 and allows fluid to flow from the lumen 252 to theexterior of the vessel 246.

Both edge-seal leak 240 (FIG. 18) and mid-seal wall leak 256 (FIG. 19)create difficult medical problems. Usually, the sealed area has enoughinitial integrity to withstand the pressure of the fluid in the lumen ofthe vessel for a short amount of time, but continued blood or fluidpressure variations within the body cause the edge-seal leak or themid-seal wall leak to occur at a later time, usually after closure ofthe surgical incision and completion of the entire surgical procedure.Post-operative internal bleeding will have severe consequences if thebleeding is not stopped quickly. Consequently, both an edge-seal leak240 and a mid-seal wall leak 256 require undertaking a second surgicalprocedure to stop those leaks. Such second surgical procedures followingimmediately on the earlier procedure induce considerable additionaltrauma and risk to the patient.

The failure mode of seals created by use of the present invention whenalso simultaneously cutting the tissue, if failure occurs, issubstantially different from the prior art edge-seal leak 240 and themid-seal wall leak 256 shown in FIGS. 18 and 19. Practical use of thepresent invention within its defined and preferred parameters has neverresulted in an edge-seal leak or a mid-seal wall leak, after creatingmany hundreds of seals. On a fundamental level, an edge-seal leak 240 ora mid-seal wall leak 256 results because the strength of at least partof the sealed area is greater than the strength of a part of the vesseladjacent to or within the sealed area, usually as a result of theadjacent vessel part or the sealed part being damaged during the tissuefusion procedure. The failure mode of the seals created by the presentinvention is considerably different, because the strength of the severedvessel adjacent to the sealed areas is not impacted to the point wherethe strength of the sealed areas is significantly less than the strengthof the vessel adjacent to the sealed areas. The failure mode created bythe present invention may be characterized as a mid-seal separation, andthe mid-seal separation is of considerably less risk than either theedge-seal leak 240 or the mid-seal wall leaks 256, for the reasonsdiscussed below.

The mid-seal separation resulting from the present invention, if such aseparation occurs at all, is illustrated in FIGS. 20-24. As shown inFIGS. 20 and 21, the vessel 21 is sealed at the sealed area 50 andsimultaneously cut at the separation line 51, according to the presentinvention. The sealed area 50 is formed by forcing portions 258 of thewalls 44 of the vessel 21 into apposition with one another at the tissueinterface 46 and by delivering heat to the compressed apposite portions258 of the walls 44 at the interface 46. The separation at theseparation line 51 is caused by continued heat application and force onthe still-pliable tissue immediately following but as a continuation oftissue sealing which is sufficient to force the working surfaces 38 and40 into contact with one another and thereby sever the sealed area 50 atthe separation line 51. The temperature of the vessel wall portions 258is sufficient to denature and coagulate the protein chains in the wallportions 258 at the interface 46 and then allow those denatured proteinschains to re-nature and reconstitute to form the high-integrity sealedarea 50 while the continued force and temperature application causes thesealed area 52 separate along the separation line 51. The fusion of thewall portions 258 at the tissue interface 46 occludes the lumen 42 ofboth severed parts of the vessel 21.

After fusion of the wall portions 258 at the interface 46 in the sealedarea 50 followed by simultaneous cutting of the sealed area 50 at theseparation line 51, the application of fluid pressure within the lumen42 on the left-hand side (as shown) sealed area 50 causes the severedvessel 21 to expand as shown in FIG. 22. The walls 44 of the vessel 21stretch and balloon outward from an edge 260 of the interface 46. Acharacteristic of the seal created by the present invention is that thestrength of the fusion at the interface 46 between the wall portions 258at the sealed areas 50 is less than the strength of the unsealed walls44 of the vessel 21 and is also less than the strength of the portions258 of the wall after they have been fused together at the sealed areas50. Even though the strength of the wall portions 258 after sealing maybe somewhat diminished as a result of the heat and pressure application,the strength of those wall portions 258 is still greater than thestrength of the fusion between the wall portions 258 at the interface46, and the strength of the fused wall portions 258 at the interface 46is still considerably greater than the normal amount of pressure appliedwithin the lumen 42 by normal physiological events. Thesecharacteristics achieve a seal of substantial integrity which is capableof withstanding fluid pressures which are considerably greater thannormal, as shown in FIG. 22, but which also provides safety andreliability if the sealed areas 50 at the end of the severed vesselshould experience a mid-seal separation.

If the fluid pressure applied within the lumen is increased beyond theexaggerated level shown in FIG. 22, the fused apposed wall portions 258at the interface 46 began to separate from one another at the edge 260without rupturing the vessel walls 44 adjacent to the sealed area 50 andwithout rupturing the separated wall portions 258 which had previouslybeen fused together at the sealed area 50, as shown in FIG. 23. Thepressure causes the sealed area 50 to experience a mid-seal separation,meaning that the previously-fused wall portions 258 separate at theinterface 46. The pressure may continue to separate thepreviously-fused, apposed wall portions 258, with the separationcontinuing longitudinally along the interface 46. The separation maycontinue along the interface 46 until the entirety of thepreviously-fused wall portions 258 have separated, at which point theocclusion of the vessel 21 is eliminated and the vessel 21 openscompletely as shown in FIG. 24.

Because the previously-fused wall portions 258 retain substantialnatural strength as a result of the present invention, a rupture throughthe wall 44 of the vessel 21 is avoided. The entire sealed area 50 willseparate in the manner shown in FIG. 24 under unusual circumstances, butneither the unaffected walls 44 nor the previously sealed wall portions258 rupture to the exterior of the vessel 21 and create a leak from thelumen 42 to the exterior of the vessel, as is the case in a prior artedge seal leak 240 (FIG. 18) or a prior art mid-seal wall leak 256 (FIG.19). The fluid-confining lumen 42 remains intact to confine the fluidwithin the vessel 21. Thus, even if the wall portions 258 at the sealedareas 50 separate, such a mid-seal separation does not result in arupture of the vessel wall 44 to permit fluid to flow from the lumen 42to the outside of the vessel 21. This type of mid-seal separation is thesame as is created from simply fusing the tissue without simultaneouslycutting the tissue, as is described in the first above-mentioned USpatent application. The capability of sealing vessels in such a way toachieve a consistent and reliable mid-seal separation as a failure modeis thought to never before have been achieved from electrosurgical orelectrothermal tissue fusion or from electrosurgical or electrothermaltissue fusion and simultaneous cutting.

The consistent and predictable mid-seal separation created by thepresent invention offers substantial advantages in redundancy. It is notunusual during surgery to create multiple sealed areas 270 and 272 whichare slightly longitudinally spaced from one another along the length ofa vessel 274, as shown in FIG. 25. The belief is that if the primary orupstream sealed area 270 ruptures or fails, the remaining secondarybackup or redundant downstream sealed area 272 will hold, thuspreventing a leak. This belief is prevalent even though a significantnumber of instances of failure of the upstream or primary sealed areaare edge-seal leaks 240 (FIG. 18) or mid-seal wall leaks 256 (FIG. 19),also shown respectively in FIGS. 26 and 27. Under circumstances of anedge-seal leak or a mid-seal wall leak, the secondary or downstreambackup sealed area 272 is totally ineffective to prevent fluid loss dueto the rupture through the wall of the vessel upstream of the backupsealed area.

Thus, the perceived benefit of sequential primary and backup seals 270and 272 created by prior art tissue sealing techniques is almost alwaysillusory. When the typical edge-seal leak 240 or the typical mid-sealwall leak 256 occurs at the primary sealed area 270, as shown in FIGS.26 and 27, respectively, the leaks 240 and 256 divert the fluid from alumen 276 of the vessel 274 to the outside of the vessel. Under suchcircumstances, the secondary or backup sealed area 272 has no ability torestrain the fluid within the lumen 276 because the leaks 240 and 256have diverted the fluid away from the backup sealed area 272. The backupsealed area 272 therefore has no ability and no utility to restrainbleeding under typical prior-art sealed-area failure-mode circumstances.The significant occurrences of prior art edge-seal leaks or mid-sealwall leaks, even if as low statistically as 20%, does not provideeffective redundancy or backup.

On the other hand as a result of using the present invention as shown inFIG. 28 to fuse and simultaneously cut the tissue at a secondary orbackup sealed area 50 b, a mid-seal separation at a primary sealed area50 a still confines the fluid within the lumen 42 of the vessel 21 andconducts that fluid within the lumen 42 to the backup sealed area 50 b.The upstream primary fused area at 50 a may be conveniently created byuse of the same instrument 22, but only to fuse the upstream primaryarea 50 a. Tissue fusion without cutting is described in the firstabove-referenced US patent application. The strength of the vessel wallsat the primary sealed area 50 a is sufficient to confine the fluidwithin the lumen 42 without rupture. Consequently, the fluid pressure isapplied to the backup sealed area 50 b where that backup sealed area 50b has the opportunity to provide effective redundancy to prevent fluidleaks from the sealed vessel 21. Practical use of the present inventionwithin its defined and preferred parameters has never resulted in anedge-seal leak or a mid-seal wall leak, after creating many hundreds ofseals. Effective redundancy and backup is therefore achieved by thepresent invention.

Although the sealed areas created by the present invention normally havesufficient strength and integrity as to achieve a relatively lowprobability of failure, the beneficial use of multiple sealssubstantially diminishes the risk of internal bleeding, even when thesecondary or backup sealed area is also simultaneously cut. Moreover,the substantially diminished risk of internal bleeding is enhanced bythe reliability of obtaining consistent seals of high integrity witheach fusion procedure performed in accordance with the presentinvention.

Another benefit of the present invention relates to the common practiceof forming overlapping seals. An overlapping seal is formed from a firstseal on a vessel in the typical manner, coupled with forming a secondseal in which the sealed area of the second seal overlaps a portion ofthe sealed area of the first seal. Overlapping sealing is typicallyapplied to seal large vessels where the perception is that additionalenergy is required because of the size of the large vessel. The secondseal may overlap the initially sealed area by approximately 50% up to100%. To do so, the first sealed area is compressed and heated again,along with any previously unsealed adjoining tissue depending upon thedegree of overlap. A 100% overlap involves performing second sealingprocedure entirely coincidentally with the initial seal.

The present invention is beneficial in performing overlapped sealingcombined with simultaneous cutting because the heat created from theimpulse of electrical power does not dissipate to the surrounding vesselwalls to a sufficient degree to damage the vessel. Reducing orminimizing the damage of the vessel walls adjacent to the seal allowssubsequent applications of energy to be effective in reinforcingprevious seals, because the vessel has not been previously damaged bythe excessive application of heat. However, when the overlapping seal iscreated, the sealed area is also simultaneously severed by theapplication of heat. Thus, the present invention is effective increating overlapping seals while simultaneously cutting the overlappedsealed areas.

The benefits and improvements of the present invention are numerous andsignificant. The efficiency of vessel fusion and simultaneous cuttingprocedures is increased by delivering the high power impulses whichcreate the heat for fusion and cutting. Reliable vessel seals arecreated considerably faster than with the prior art tissue fusiontechniques now commonly used, and the vessel is cut in such a way whichdoes not compromise or negatively affect the strength of the sealcreated. The vessel seals are significantly stronger and more reliablethan the seals created using common prior art tissue fusion or combinedtissue fusion and cutting devices. The mid-seal separation failure modeconfines the fluid within the vessel, thereby simplifying the process ofre-sealing the vessel. Multiple sequential seals on a single vesselensure that the probability of ultimate seal failure is extremely lowbecause the mid-seal separation failure mode allows the multiplesequential seals to achieve effective redundancy, unlike known prior arttissue fusion or combined tissue fusion and cutting devices. Overlappingsealing and simultaneous cutting may also be beneficially appliedbecause of the ability of the present invention to confine the energy tothe sealed area without significantly spreading that energy to damageadjacent tissues and because the initial energy application has notsubstantially compromised the tissue strength or pliability of thesealed area. An immediate mid-seal separation allows the seal andsimultaneous cutting procedure to be corrected.

The significance of these and many other improvements and advantageswill become apparent upon gaining a full appreciation of theramifications and improvements of the present invention. Preferredembodiments of the invention and many of its improvements have beendescribed with a degree of particularity. The description is ofpreferred examples of implementing the invention, but the description isnot necessarily intended to limit the scope of the invention. The scopeof the invention is defined by the following claims.

What is claimed is:
 1. A method of electrothermally fusing togetherpieces of tissue at an interface and simultaneously cutting the fusedtissue along a linear path through the interface, comprising:compressing the tissue pieces together at the interface sufficiently forfusing the tissue pieces together and for cutting the fused tissuepieces in the linear path through the fused tissue at the interface;delivering an impulse of electrical power of no greater than 4.0 secondstime duration which contains sufficient energy to fuse the tissue piecestogether at the interface and to simultaneously cut the fused tissue inthe linear path through the fused tissue at the interface within thetime duration of the electrical power impulse; converting the electricalpower impulse into thermal energy applied at the interface to fuse thetissue pieces and to simultaneously cut the fused tissue pieces in thelinear path through the interface; and regulating the temperature of thethermal energy applied at the interface in a range of 200° C. to 320° C.while fusing and simultaneously cutting the tissue pieces at theinterface by controlling characteristics of the electrical powerimpulse.
 2. A method as defined in claim 1, wherein the electrical powerimpulse has a time duration of no greater than 2.0 seconds.
 3. A methodas defined in claim 1, wherein the electrical power impulse has a timeduration of approximately 1.5 seconds.
 4. A method as defined in claim1, wherein the electrical power impulse has a time duration in the rangeof 1.5 seconds to 2.0 seconds.
 5. A method as defined in claim 4,further comprising: releasing compression of the interface immediatelyafter termination of the electrical power impulse.
 6. A method asdefined in claim 1, further comprising: elevating the temperature of thethermal energy applied at the compressed interface at a rate of between150° C. per second to 500° C. per second or greater from energycontained in the electrical power impulse.
 7. A method as defined inclaim 1, further comprising: producing an energy density in the range of388 W/cm2 to 465 W/cm2 of area of the compressed interface from theelectrical power impulse.
 8. A method as defined in claim 1, furthercomprising: producing an energy density of at least 233 W/cm2 of area ofthe compressed interface from the electrical power impulse.
 9. A methodas defined in claim 1, further comprising: producing an energy densityof at least 388 W/cm2 of area of the compressed interface from theelectrical power impulse.
 10. A method as defined in claim 1, furthercomprising: cutting the fused tissue pieces in a curved linear paththrough the interface.
 11. A method as defined in claim 1, furthercomprising: compressing the tissue pieces together at the interface toachieve essentially a zero thickness of the heated and compressed tissuepieces along the linear path.
 12. A method as defined in claim 1,further comprising: producing pressure of the least 0.88 N/mm2 over theeffective area of the fused interface while compressing the tissuepieces.
 13. A method as defined in claim 1, further comprising:compressing the tissue pieces at the interface by contacting the tissuepieces on opposite sides of the interface by working surfaces of jaws;applying the thermal energy to heat the jaws; and transferring thermalenergy from the working surfaces to the compressed interface of thetissue pieces.
 14. A method as defined in claim 13, further comprising:forming electrical power impulse from direct current; and applying thedirect current of the electrical power impulse to heat each jaw.
 15. Amethod as defined in claim 13, wherein each working surface is formed ofceramic material and each working surface has a smoothness defined by anRa of 0.40 microns or less.
 16. A method as defined in claim 13, whereineach of the working surfaces extends in a dimension, and furthercomprising: releasing compression of the interface after fusion andsimultaneous cutting by moving the working surfaces away from the fusedand cut interface with the dimensions of each working surface extendingparallel to one another.
 17. A method as defined in claim 13, furthercomprising: delivering an electrical power impulse to a heating elementwithin each jaw; and separately regulating characteristics theelectrical power impulse delivered to the heating element within eachjaw to regulate the temperature of thermal energy applied by the workingsurface from each jaw separately.
 18. A method as defined in claim 1,further comprising: releasing compression of the interface immediatelyafter fusion without inducing shear forces on the fused interface.
 19. Amethod as defined in claim 1, further comprising: creating strengthbetween the fused tissue pieces at the interface from the fusion whichis less than the inherent strength of each tissue piece at the fusedinterface to allow separation of the tissue pieces at the interfacebefore breaching the tissue pieces at or adjoining the fused interface.20. A method as defined in claim 1, wherein pieces of tissue areapposite walls of a vessel, and the compressed tissue thicknesssufficient to fuse the opposite walls of the blood vessel is 0.05 mm to0.10 mm.
 21. A method as defined in claim 20, wherein the vessel has adiameter of up to 8 mm.